diff --git a/examples/cwebp.c b/examples/cwebp.c
index 2d1f076d..378dfa85 100644
--- a/examples/cwebp.c
+++ b/examples/cwebp.c
@@ -31,13 +31,13 @@
 #include "./wicdec.h"
 
 #ifndef WEBP_DLL
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
 extern void* VP8GetCPUInfo;   // opaque forward declaration.
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 #endif  // WEBP_DLL
diff --git a/examples/dwebp.c b/examples/dwebp.c
index fca9c9a7..c1470466 100644
--- a/examples/dwebp.c
+++ b/examples/dwebp.c
@@ -49,13 +49,13 @@
 
 static int verbose = 0;
 #ifndef WEBP_DLL
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
 extern void* VP8GetCPUInfo;   // opaque forward declaration.
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 #endif  // WEBP_DLL
diff --git a/examples/example_util.h b/examples/example_util.h
index 0122fd3c..b478025f 100644
--- a/examples/example_util.h
+++ b/examples/example_util.h
@@ -15,7 +15,7 @@
 
 #include "webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -29,7 +29,7 @@ int ExUtilReadFile(const char* const file_name,
 int ExUtilWriteFile(const char* const file_name,
                     const uint8_t* data, size_t data_size);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/examples/gif2webp_util.h b/examples/gif2webp_util.h
index fd540459..95313e6c 100644
--- a/examples/gif2webp_util.h
+++ b/examples/gif2webp_util.h
@@ -18,7 +18,7 @@
 
 #include "webp/mux.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -73,7 +73,7 @@ WebPMuxError WebPFrameCacheFlushAll(WebPFrameCache* const cache, int verbose,
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/examples/jpegdec.h b/examples/jpegdec.h
index 156620f2..cc6e3a19 100644
--- a/examples/jpegdec.h
+++ b/examples/jpegdec.h
@@ -15,7 +15,7 @@
 #include <stdio.h>
 #include "webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -28,7 +28,7 @@ struct WebPPicture;
 int ReadJPEG(FILE* in_file, struct WebPPicture* const pic,
              struct Metadata* const metadata);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/examples/metadata.h b/examples/metadata.h
index 989a43eb..7f272c6b 100644
--- a/examples/metadata.h
+++ b/examples/metadata.h
@@ -15,7 +15,7 @@
 
 #include "webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -40,7 +40,7 @@ void MetadataFree(Metadata* const metadata);
 int MetadataCopy(const char* metadata, size_t metadata_len,
                  MetadataPayload* const payload);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/examples/pngdec.h b/examples/pngdec.h
index 80c142d2..aeeb02ad 100644
--- a/examples/pngdec.h
+++ b/examples/pngdec.h
@@ -14,7 +14,7 @@
 
 #include <stdio.h>
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -28,7 +28,7 @@ struct WebPPicture;
 int ReadPNG(FILE* in_file, struct WebPPicture* const pic, int keep_alpha,
             struct Metadata* const metadata);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/examples/tiffdec.h b/examples/tiffdec.h
index cde1534f..d6f90958 100644
--- a/examples/tiffdec.h
+++ b/examples/tiffdec.h
@@ -12,7 +12,7 @@
 #ifndef WEBP_EXAMPLES_TIFFDEC_H_
 #define WEBP_EXAMPLES_TIFFDEC_H_
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -27,7 +27,7 @@ int ReadTIFF(const char* const filename,
              struct WebPPicture* const pic, int keep_alpha,
              struct Metadata* const metadata);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/examples/wicdec.h b/examples/wicdec.h
index 6d797ce0..94d44b36 100644
--- a/examples/wicdec.h
+++ b/examples/wicdec.h
@@ -12,7 +12,7 @@
 #ifndef WEBP_EXAMPLES_WICDEC_H_
 #define WEBP_EXAMPLES_WICDEC_H_
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -27,7 +27,7 @@ int ReadPictureWithWIC(const char* const filename,
                        struct WebPPicture* const pic, int keep_alpha,
                        struct Metadata* const metadata);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/dec/alphai.h b/src/dec/alphai.h
index 3fbae4ae..5fa230ca 100644
--- a/src/dec/alphai.h
+++ b/src/dec/alphai.h
@@ -17,7 +17,7 @@
 #include "./webpi.h"
 #include "../utils/filters.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -48,7 +48,7 @@ void ALPHDelete(ALPHDecoder* const dec);
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/dec/decode_vp8.h b/src/dec/decode_vp8.h
index 25aec324..b9337bbe 100644
--- a/src/dec/decode_vp8.h
+++ b/src/dec/decode_vp8.h
@@ -16,7 +16,7 @@
 
 #include "../webp/decode.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -178,7 +178,7 @@ WEBP_EXTERN(int) VP8LGetInfo(
     const uint8_t* data, size_t data_size,  // data available so far
     int* const width, int* const height, int* const has_alpha);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/dec/vp8i.h b/src/dec/vp8i.h
index bb438626..410b403c 100644
--- a/src/dec/vp8i.h
+++ b/src/dec/vp8i.h
@@ -21,7 +21,7 @@
 #include "../utils/thread.h"
 #include "../dsp/dsp.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -352,7 +352,7 @@ int VP8DecodeLayer(VP8Decoder* const dec);
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/dec/vp8li.h b/src/dec/vp8li.h
index aa132a64..afa294db 100644
--- a/src/dec/vp8li.h
+++ b/src/dec/vp8li.h
@@ -22,7 +22,7 @@
 #include "../utils/huffman.h"
 #include "../webp/format_constants.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -130,7 +130,7 @@ void VP8LDelete(VP8LDecoder* const dec);
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/dec/webpi.h b/src/dec/webpi.h
index 4ae0bfc5..d915f5ef 100644
--- a/src/dec/webpi.h
+++ b/src/dec/webpi.h
@@ -14,7 +14,7 @@
 #ifndef WEBP_DEC_WEBPI_H_
 #define WEBP_DEC_WEBPI_H_
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -109,7 +109,7 @@ void WebPGrabDecBuffer(WebPDecBuffer* const src, WebPDecBuffer* const dst);
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/dsp/dsp.h b/src/dsp/dsp.h
index 98782c88..3be783af 100644
--- a/src/dsp/dsp.h
+++ b/src/dsp/dsp.h
@@ -16,7 +16,7 @@
 
 #include "../webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -217,7 +217,7 @@ void WebPInitPremultiplyNEON(void);
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/dsp/lossless.h b/src/dsp/lossless.h
index 81196063..0f1d4420 100644
--- a/src/dsp/lossless.h
+++ b/src/dsp/lossless.h
@@ -18,7 +18,7 @@
 #include "../webp/types.h"
 #include "../webp/decode.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -213,7 +213,7 @@ void VP8LBundleColorMap(const uint8_t* const row, int width,
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/dsp/yuv.h b/src/dsp/yuv.h
index 3ad434ee..dd778f9c 100644
--- a/src/dsp/yuv.h
+++ b/src/dsp/yuv.h
@@ -55,7 +55,7 @@
 //------------------------------------------------------------------------------
 // YUV -> RGB conversion
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -310,7 +310,7 @@ static WEBP_INLINE int VP8_RGB_TO_V(int r, int g, int b, int rounding) {
 
 #endif    // USE_YUVj
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/enc/backward_references.h b/src/enc/backward_references.h
index c89789bf..e1c75f04 100644
--- a/src/enc/backward_references.h
+++ b/src/enc/backward_references.h
@@ -18,7 +18,7 @@
 #include "../webp/types.h"
 #include "../webp/format_constants.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -145,7 +145,7 @@ int VP8LCalculateEstimateForCacheSize(const uint32_t* const argb,
                                       int xsize, int ysize,
                                       int* const best_cache_bits);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }
 #endif
 
diff --git a/src/enc/cost.h b/src/enc/cost.h
index 7d7c2c79..3cbad1ae 100644
--- a/src/enc/cost.h
+++ b/src/enc/cost.h
@@ -16,7 +16,7 @@
 
 #include "./vp8enci.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -44,7 +44,7 @@ extern const uint16_t VP8FixedCostsI4[NUM_BMODES][NUM_BMODES][NUM_BMODES];
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/enc/histogram.h b/src/enc/histogram.h
index 583b5a4f..4d346a85 100644
--- a/src/enc/histogram.h
+++ b/src/enc/histogram.h
@@ -24,7 +24,7 @@
 #include "../webp/format_constants.h"
 #include "../webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -94,7 +94,7 @@ int VP8LGetHistoImageSymbols(int xsize, int ysize,
                              VP8LHistogramSet* const image_in,
                              uint16_t* const histogram_symbols);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }
 #endif
 
diff --git a/src/enc/vp8enci.h b/src/enc/vp8enci.h
index be7b9a80..20d0af92 100644
--- a/src/enc/vp8enci.h
+++ b/src/enc/vp8enci.h
@@ -20,7 +20,7 @@
 #include "../utils/bit_writer.h"
 #include "../utils/thread.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -563,7 +563,7 @@ int VP8FilterStrengthFromDelta(int sharpness, int delta);
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/enc/vp8li.h b/src/enc/vp8li.h
index 01f01f57..96d6faed 100644
--- a/src/enc/vp8li.h
+++ b/src/enc/vp8li.h
@@ -19,7 +19,7 @@
 #include "../webp/encode.h"
 #include "../webp/format_constants.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -63,7 +63,7 @@ WebPEncodingError VP8LEncodeStream(const WebPConfig* const config,
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/mux/muxi.h b/src/mux/muxi.h
index 995e3f28..072fd061 100644
--- a/src/mux/muxi.h
+++ b/src/mux/muxi.h
@@ -19,7 +19,7 @@
 #include "../dec/vp8li.h"
 #include "../webp/mux.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -223,7 +223,7 @@ WebPMuxError MuxValidate(const WebPMux* const mux);
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/utils/alpha_processing.h b/src/utils/alpha_processing.h
index 5dcc097d..80e1ae45 100644
--- a/src/utils/alpha_processing.h
+++ b/src/utils/alpha_processing.h
@@ -16,7 +16,7 @@
 
 #include "../webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -39,7 +39,7 @@ void WebPMultRows(uint8_t* ptr, int stride,
                   const uint8_t* alpha, int alpha_stride,
                   int width, int num_rows, int inverse);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/utils/bit_reader.h b/src/utils/bit_reader.h
index 52306393..98df98a7 100644
--- a/src/utils/bit_reader.h
+++ b/src/utils/bit_reader.h
@@ -21,7 +21,7 @@
 #endif
 #include "../webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -327,7 +327,7 @@ static WEBP_INLINE void VP8LSetBitPos(VP8LBitReader* const br, int val) {
 // Advances the read buffer by 4 bytes to make room for reading next 32 bits.
 void VP8LFillBitWindow(VP8LBitReader* const br);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/utils/bit_writer.h b/src/utils/bit_writer.h
index cbb095c1..89a9ead4 100644
--- a/src/utils/bit_writer.h
+++ b/src/utils/bit_writer.h
@@ -16,7 +16,7 @@
 
 #include "../webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -118,7 +118,7 @@ void VP8LWriteBits(VP8LBitWriter* const bw, int n_bits, uint32_t bits);
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/utils/color_cache.h b/src/utils/color_cache.h
index e5a0bd6f..0f824ed4 100644
--- a/src/utils/color_cache.h
+++ b/src/utils/color_cache.h
@@ -17,7 +17,7 @@
 
 #include "../webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -63,7 +63,7 @@ void VP8LColorCacheClear(VP8LColorCache* const color_cache);
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }
 #endif
 
diff --git a/src/utils/filters.h b/src/utils/filters.h
index ae8ef85d..dde39cb5 100644
--- a/src/utils/filters.h
+++ b/src/utils/filters.h
@@ -16,7 +16,7 @@
 
 #include "../webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -52,7 +52,7 @@ extern const WebPUnfilterFunc WebPUnfilters[WEBP_FILTER_LAST];
 WEBP_FILTER_TYPE EstimateBestFilter(const uint8_t* data,
                                     int width, int height, int stride);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/utils/huffman.h b/src/utils/huffman.h
index f219c541..e8afd27f 100644
--- a/src/utils/huffman.h
+++ b/src/utils/huffman.h
@@ -17,7 +17,7 @@
 #include <assert.h>
 #include "../webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -80,7 +80,7 @@ int HuffmanCodeLengthsToCodes(const int* const code_lengths,
                               int code_lengths_size, int* const huff_codes);
 
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/utils/huffman_encode.h b/src/utils/huffman_encode.h
index 0b81f470..ee51c68c 100644
--- a/src/utils/huffman_encode.h
+++ b/src/utils/huffman_encode.h
@@ -16,7 +16,7 @@
 
 #include "../webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -42,7 +42,7 @@ int VP8LCreateCompressedHuffmanTree(const HuffmanTreeCode* const tree,
 int VP8LCreateHuffmanTree(int* const histogram, int tree_depth_limit,
                           HuffmanTreeCode* const tree);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }
 #endif
 
diff --git a/src/utils/quant_levels.h b/src/utils/quant_levels.h
index 2d90828d..1cb5a32c 100644
--- a/src/utils/quant_levels.h
+++ b/src/utils/quant_levels.h
@@ -18,7 +18,7 @@
 
 #include "../webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -29,7 +29,7 @@ extern "C" {
 int QuantizeLevels(uint8_t* const data, int width, int height, int num_levels,
                    uint64_t* const sse);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/utils/quant_levels_dec.h b/src/utils/quant_levels_dec.h
index a707224d..0288383a 100644
--- a/src/utils/quant_levels_dec.h
+++ b/src/utils/quant_levels_dec.h
@@ -16,7 +16,7 @@
 
 #include "../webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -27,7 +27,7 @@ extern "C" {
 int DequantizeLevels(uint8_t* const data, int width, int height,
                      int row, int num_rows);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/utils/random.h b/src/utils/random.h
index 32632d3d..08a83e96 100644
--- a/src/utils/random.h
+++ b/src/utils/random.h
@@ -17,7 +17,7 @@
 #include <assert.h>
 #include "../webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -55,7 +55,7 @@ static WEBP_INLINE int VP8RandomBits(VP8Random* const rg, int num_bits) {
   return VP8RandomBits2(rg, num_bits, rg->amp_);
 }
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/utils/rescaler.h b/src/utils/rescaler.h
index a5b40d45..68e49cee 100644
--- a/src/utils/rescaler.h
+++ b/src/utils/rescaler.h
@@ -14,7 +14,7 @@
 #ifndef WEBP_UTILS_RESCALER_H_
 #define WEBP_UTILS_RESCALER_H_
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -77,7 +77,7 @@ int WebPRescalerExport(WebPRescaler* const rescaler);
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/utils/thread.h b/src/utils/thread.h
index c2b92c9f..aef33bda 100644
--- a/src/utils/thread.h
+++ b/src/utils/thread.h
@@ -18,7 +18,7 @@
 #include "config.h"
 #endif
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -90,7 +90,7 @@ void WebPWorkerEnd(WebPWorker* const worker);
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/utils/utils.h b/src/utils/utils.h
index e10aeeb9..8bdf0f03 100644
--- a/src/utils/utils.h
+++ b/src/utils/utils.h
@@ -19,7 +19,7 @@
 
 #include "../webp/types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -76,7 +76,7 @@ static WEBP_INLINE void PutLE32(uint8_t* const data, uint32_t val) {
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/webp/decode.h b/src/webp/decode.h
index ad5125ac..0c3b62e2 100644
--- a/src/webp/decode.h
+++ b/src/webp/decode.h
@@ -16,7 +16,7 @@
 
 #include "./types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -484,7 +484,7 @@ WEBP_EXTERN(WebPIDecoder*) WebPIDecode(const uint8_t* data, size_t data_size,
 WEBP_EXTERN(VP8StatusCode) WebPDecode(const uint8_t* data, size_t data_size,
                                       WebPDecoderConfig* config);
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/webp/demux.h b/src/webp/demux.h
index 09b5a7a8..2da3239d 100644
--- a/src/webp/demux.h
+++ b/src/webp/demux.h
@@ -50,7 +50,7 @@
 
 #include "./mux_types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -217,7 +217,7 @@ WEBP_EXTERN(void) WebPDemuxReleaseChunkIterator(WebPChunkIterator* iter);
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/webp/encode.h b/src/webp/encode.h
index 0b8fe4c9..7a428b4e 100644
--- a/src/webp/encode.h
+++ b/src/webp/encode.h
@@ -16,7 +16,7 @@
 
 #include "./types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -491,7 +491,7 @@ WEBP_EXTERN(int) WebPEncode(const WebPConfig* config, WebPPicture* picture);
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/webp/mux.h b/src/webp/mux.h
index 37884d60..eb57f51c 100644
--- a/src/webp/mux.h
+++ b/src/webp/mux.h
@@ -51,7 +51,7 @@
 
 #include "./mux_types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -370,7 +370,7 @@ WEBP_EXTERN(WebPMuxError) WebPMuxAssemble(WebPMux* mux,
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif
 
diff --git a/src/webp/mux_types.h b/src/webp/mux_types.h
index 94d8806e..c94043a3 100644
--- a/src/webp/mux_types.h
+++ b/src/webp/mux_types.h
@@ -18,7 +18,7 @@
 #include <string.h>  // memset()
 #include "./types.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -90,7 +90,7 @@ static WEBP_INLINE int WebPDataCopy(const WebPData* src, WebPData* dst) {
   return 1;
 }
 
-#if defined(__cplusplus) || defined(c_plusplus)
+#ifdef __cplusplus
 }    // extern "C"
 #endif