diff --git a/CMakeLists.txt b/CMakeLists.txt
index 37619652..556241a5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -22,6 +22,9 @@ if(NOT EMSCRIPTEN)
 endif()
 option(WEBP_ENABLE_SIMD "Enable any SIMD optimization."
        ${WEBP_ENABLE_SIMD_DEFAULT})
+# Emscripten supports SSE builds using its compatibility headers, by default it
+# will use SSE4 if WEBP_ENABLE_WASM_SIMD is OFF and WEBP_ENABLE_SIMD is ON.
+option(WEBP_ENABLE_WASM_SIMD "Enable WebAssembly SIMD optimizations" OFF)
 option(WEBP_BUILD_ANIM_UTILS "Build animation utilities." ON)
 option(WEBP_BUILD_CWEBP "Build the cwebp command line tool." ON)
 option(WEBP_BUILD_DWEBP "Build the dwebp command line tool." ON)
@@ -48,7 +51,6 @@ endif()
 if(WEBP_BUILD_WEBP_JS)
   set(WEBP_BUILD_ANIM_UTILS OFF)
   set(WEBP_BUILD_CWEBP OFF)
-  set(WEBP_BUILD_DWEBP OFF)
   set(WEBP_BUILD_GIF2WEBP OFF)
   set(WEBP_BUILD_IMG2WEBP OFF)
   set(WEBP_BUILD_VWEBP OFF)
@@ -80,6 +82,9 @@ include(GNUInstallDirs)
 if(WEBP_ENABLE_SWAP_16BIT_CSP)
   add_definitions(-DWEBP_SWAP_16BIT_CSP=1)
 endif()
+if(WEBP_ENABLE_WASM_SIMD)
+  add_definitions(-DWEBP_ENABLE_WASM_SIMD)
+endif()
 
 if(NOT WEBP_BITTRACE STREQUAL "0")
   add_definitions(-DBITTRACE=${WEBP_BITTRACE})
diff --git a/cmake/config.h.in b/cmake/config.h.in
index 3770935c..60cbe53a 100644
--- a/cmake/config.h.in
+++ b/cmake/config.h.in
@@ -108,6 +108,9 @@
 /* Set to 1 if JPEG library is installed */
 #cmakedefine WEBP_HAVE_JPEG 1
 
+/* Set to 1 if Wasm SIMD is supported */
+#cmakedefine WEBP_HAVE_WASM_SIMD
+
 /* Set to 1 if NEON is supported */
 #cmakedefine WEBP_HAVE_NEON
 
diff --git a/cmake/cpu.cmake b/cmake/cpu.cmake
index bc0dbc98..d1e28d25 100644
--- a/cmake/cpu.cmake
+++ b/cmake/cpu.cmake
@@ -36,9 +36,9 @@ function(webp_check_compiler_flag WEBP_SIMD_FLAG ENABLE_SIMD)
 endfunction()
 
 # those are included in the names of WEBP_USE_* in c++ code.
-set(WEBP_SIMD_FLAGS "SSE41;SSE2;MIPS32;MIPS_DSP_R2;NEON;MSA")
+set(WEBP_SIMD_FLAGS "WASM_SIMD;SSE41;SSE2;MIPS32;MIPS_DSP_R2;NEON;MSA")
 set(WEBP_SIMD_FILE_EXTENSIONS
-    "_sse41.c;_sse2.c;_mips32.c;_mips_dsp_r2.c;_neon.c;_msa.c")
+    "_wasm.c;_sse41.c;_sse2.c;_mips32.c;_mips_dsp_r2.c;_neon.c;_msa.c")
 if(MSVC AND CMAKE_C_COMPILER_ID STREQUAL "MSVC")
   # With at least Visual Studio 12 (2013)+ /arch is not necessary to build SSE2
   # or SSE4 code unless a lesser /arch is forced. MSVC does not have a SSE4
@@ -53,9 +53,9 @@ if(MSVC AND CMAKE_C_COMPILER_ID STREQUAL "MSVC")
   set(SIMD_DISABLE_FLAGS)
 else()
   set(SIMD_ENABLE_FLAGS
-      "-msse4.1;-msse2;-mips32;-mdspr2;-mfpu=neon;-mmsa")
+      "-msimd128;-msse4.1;-msse2;-mips32;-mdspr2;-mfpu=neon;-mmsa")
   set(SIMD_DISABLE_FLAGS
-      "-mno-sse4.1;-mno-sse2;;-mno-dspr2;;-mno-msa")
+      "-mno-simd128;-mno-sse4.1;-mno-sse2;;-mno-dspr2;;-mno-msa")
 endif()
 
 set(WEBP_SIMD_FILES_TO_NOT_INCLUDE)
@@ -77,7 +77,12 @@ math(EXPR WEBP_SIMD_FLAGS_RANGE "${WEBP_SIMD_FLAGS_LENGTH} - 1")
 foreach(I_SIMD RANGE ${WEBP_SIMD_FLAGS_RANGE})
   # With Emscripten 2.0.9 -msimd128 -mfpu=neon will enable NEON, but the
   # source will fail to compile.
-  if(EMSCRIPTEN AND ${I_SIMD} GREATER_EQUAL 2)
+  if(EMSCRIPTEN AND ${I_SIMD} GREATER_EQUAL 5)
+    break()
+  endif()
+  # Emscripten supports SSE via compat headers, if WEBP_ENABLED_WASM_SIMD is
+  # specified skip testing those (because it will succeed).
+  if (EMSCRIPTEN AND ${I_SIMD} GREATER_EQUAL 1 AND ${WEBP_ENABLE_WASM_SIMD})
     break()
   endif()
 
@@ -91,6 +96,7 @@ foreach(I_SIMD RANGE ${WEBP_SIMD_FLAGS_RANGE})
   webp_check_compiler_flag(${WEBP_SIMD_FLAG} ${WEBP_ENABLE_SIMD})
   if(NOT WEBP_HAVE_${WEBP_SIMD_FLAG})
     list(GET SIMD_ENABLE_FLAGS ${I_SIMD} SIMD_COMPILE_FLAG)
+    # This enables using Emscripten's SSE compatibility headers.
     if(EMSCRIPTEN)
       set(SIMD_COMPILE_FLAG "-msimd128 ${SIMD_COMPILE_FLAG}")
     endif()
diff --git a/src/dsp/Makefile.am b/src/dsp/Makefile.am
index 766bb0a7..8d88ee7d 100644
--- a/src/dsp/Makefile.am
+++ b/src/dsp/Makefile.am
@@ -13,6 +13,7 @@ noinst_LTLIBRARIES += libwebpdsp_mips32.la
 noinst_LTLIBRARIES += libwebpdspdecode_mips32.la
 noinst_LTLIBRARIES += libwebpdsp_mips_dsp_r2.la
 noinst_LTLIBRARIES += libwebpdspdecode_mips_dsp_r2.la
+noinst_LTLIBRARIES += libwebpdspdecode_wasm.la
 
 if BUILD_LIBWEBPDECODER
   noinst_LTLIBRARIES += libwebpdspdecode.la
@@ -106,6 +107,8 @@ libwebpdspdecode_mips_dsp_r2_la_SOURCES += yuv_mips_dsp_r2.c
 libwebpdspdecode_mips_dsp_r2_la_CPPFLAGS = $(libwebpdsp_mips_dsp_r2_la_CPPFLAGS)
 libwebpdspdecode_mips_dsp_r2_la_CFLAGS = $(libwebpdsp_mips_dsp_r2_la_CFLAGS)
 
+libwebpdspdecode_wasm_la_SOURCES = dec_wasm.c
+
 libwebpdsp_sse2_la_SOURCES =
 libwebpdsp_sse2_la_SOURCES += cost_sse2.c
 libwebpdsp_sse2_la_SOURCES += enc_sse2.c
diff --git a/src/dsp/cpu.c b/src/dsp/cpu.c
index 3145e190..3058942b 100644
--- a/src/dsp/cpu.c
+++ b/src/dsp/cpu.c
@@ -26,8 +26,10 @@
 // SSE2 detection.
 //
 
+// Skip SSE detection if using Wasm SIMD build.
+#if defined(WEBP_USE_WASM_SIMD)
 // apple/darwin gcc-4.0.1 defines __PIC__, but not __pic__ with -fPIC.
-#if (defined(__pic__) || defined(__PIC__)) && defined(__i386__)
+#elif (defined(__pic__) || defined(__PIC__)) && defined(__i386__)
 static WEBP_INLINE void GetCPUInfo(int cpu_info[4], int info_type) {
   __asm__ volatile (
     "mov %%ebx, %%edi\n"
@@ -69,8 +71,10 @@ static WEBP_INLINE void GetCPUInfo(int cpu_info[4], int info_type) {
 
 #endif
 
+// Skip xgetbv definition if using Wasm SIMD build.
+#if defined(WEBP_USE_WASM_SIMD)
 // NaCl has no support for xgetbv or the raw opcode.
-#if !defined(__native_client__) && (defined(__i386__) || defined(__x86_64__))
+#elif !defined(__native_client__) && (defined(__i386__) || defined(__x86_64__))
 static WEBP_INLINE uint64_t xgetbv(void) {
   const uint32_t ecx = 0;
   uint32_t eax, edx;
@@ -100,7 +104,13 @@ static WEBP_INLINE uint64_t xgetbv(void) {
 #define xgetbv() 0U  // no AVX for older x64 or unrecognized toolchains.
 #endif
 
-#if defined(__i386__) || defined(__x86_64__) || defined(WEBP_HAVE_MSC_CPUID)
+#if defined(WEBP_USE_WASM_SIMD)
+static int wasmCPUInfo(CPUFeature feature) {
+  if (feature != kWasmSIMD) return 0;
+  return 1;
+}
+VP8CPUInfo VP8GetCPUInfo = wasmCPUInfo;
+#elif defined(__i386__) || defined(__x86_64__) || defined(WEBP_HAVE_MSC_CPUID)
 
 // helper function for run-time detection of slow SSSE3 platforms
 static int CheckSlowModel(int info) {
diff --git a/src/dsp/dec.c b/src/dsp/dec.c
index 537c7012..5ff3c0c2 100644
--- a/src/dsp/dec.c
+++ b/src/dsp/dec.c
@@ -740,6 +740,7 @@ extern void VP8DspInitNEON(void);
 extern void VP8DspInitMIPS32(void);
 extern void VP8DspInitMIPSdspR2(void);
 extern void VP8DspInitMSA(void);
+extern void VP8DspInitWasmSIMD(void);
 
 WEBP_DSP_INIT_FUNC(VP8DspInit) {
   VP8InitClipTables();
@@ -831,6 +832,11 @@ WEBP_DSP_INIT_FUNC(VP8DspInit) {
     if (VP8GetCPUInfo(kMSA)) {
       VP8DspInitMSA();
     }
+#endif
+#if defined(WEBP_USE_WASM_SIMD)
+    if (VP8GetCPUInfo(kWasmSIMD)) {
+      VP8DspInitWasmSIMD();
+    }
 #endif
   }
 
diff --git a/src/dsp/dec_wasm.c b/src/dsp/dec_wasm.c
new file mode 100644
index 00000000..89166b6c
--- /dev/null
+++ b/src/dsp/dec_wasm.c
@@ -0,0 +1,32 @@
+// Copyright 2021 Google Inc. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+// -----------------------------------------------------------------------------
+//
+// WebAssembly (Wasm) version of some decoding functions.
+//
+// This will contain Wasm implementation of some decoding functions.
+
+#include "./dsp.h"
+
+#if defined(WEBP_USE_WASM_SIMD)
+
+//------------------------------------------------------------------------------
+// Entry point
+
+extern void VP8DspInitWasmSIMD(void);
+
+WEBP_TSAN_IGNORE_FUNCTION void VP8DspInitWasmSIMD(void) {
+  // TODO(crbug.com/v8/12371): No special implementation for Wasm yet, will be
+  // added later.
+}
+
+#else
+
+WEBP_DSP_INIT_STUB(VP8DspInitWasmSIMD)
+
+#endif  // WEBP_USE_WASM_SIMD
diff --git a/src/dsp/dsp.h b/src/dsp/dsp.h
index c4f57e4d..02bae2a8 100644
--- a/src/dsp/dsp.h
+++ b/src/dsp/dsp.h
@@ -80,6 +80,11 @@ extern "C" {
 #endif
 #endif
 
+#if (defined(EMSCRIPTEN) || defined(WEBP_HAVE_WASM_SIMD)) && \
+    defined(__wasm_simd128__) && defined(WEBP_ENABLE_WASM_SIMD)
+#define WEBP_USE_WASM_SIMD
+#endif
+
 // WEBP_HAVE_* are used to indicate the presence of the instruction set in dsp
 // files without intrinsics, allowing the corresponding Init() to be called.
 // Files containing intrinsics will need to be built targeting the instruction
@@ -257,7 +262,8 @@ typedef enum {
   kNEON,
   kMIPS32,
   kMIPSdspR2,
-  kMSA
+  kMSA,
+  kWasmSIMD
 } CPUFeature;
 // returns true if the CPU supports the feature.
 typedef int (*VP8CPUInfo)(CPUFeature feature);