diff --git a/src/dec/frame_dec.c b/src/dec/frame_dec.c
index 514e85b5..a9d5430d 100644
--- a/src/dec/frame_dec.c
+++ b/src/dec/frame_dec.c
@@ -400,7 +400,9 @@ static void DitherRow(VP8Decoder* const dec) {
 #define MACROBLOCK_VPOS(mb_y)  ((mb_y) * 16)    // vertical position of a MB
 
 // Finalize and transmit a complete row. Return false in case of user-abort.
-static int FinishRow(VP8Decoder* const dec, VP8Io* const io) {
+static int FinishRow(void* arg1, void* arg2) {
+  VP8Decoder* const dec = (VP8Decoder*)arg1;
+  VP8Io* const io = (VP8Io*)arg2;
   int ok = 1;
   const VP8ThreadContext* const ctx = &dec->thread_ctx_;
   const int cache_id = ctx->id_;
@@ -647,7 +649,7 @@ static int InitThreadContext(VP8Decoder* const dec) {
     }
     worker->data1 = dec;
     worker->data2 = (void*)&dec->thread_ctx_.io_;
-    worker->hook = (WebPWorkerHook)FinishRow;
+    worker->hook = FinishRow;
     dec->num_caches_ =
       (dec->filter_type_ > 0) ? MT_CACHE_LINES : MT_CACHE_LINES - 1;
   } else {
diff --git a/src/enc/alpha_enc.c b/src/enc/alpha_enc.c
index 7e8d87f2..dce9ca95 100644
--- a/src/enc/alpha_enc.c
+++ b/src/enc/alpha_enc.c
@@ -361,7 +361,8 @@ static int EncodeAlpha(VP8Encoder* const enc,
 //------------------------------------------------------------------------------
 // Main calls
 
-static int CompressAlphaJob(VP8Encoder* const enc, void* dummy) {
+static int CompressAlphaJob(void* arg1, void* dummy) {
+  VP8Encoder* const enc = (VP8Encoder*)arg1;
   const WebPConfig* config = enc->config_;
   uint8_t* alpha_data = NULL;
   size_t alpha_size = 0;
@@ -394,7 +395,7 @@ void VP8EncInitAlpha(VP8Encoder* const enc) {
     WebPGetWorkerInterface()->Init(worker);
     worker->data1 = enc;
     worker->data2 = NULL;
-    worker->hook = (WebPWorkerHook)CompressAlphaJob;
+    worker->hook = CompressAlphaJob;
   }
 }
 
diff --git a/src/enc/analysis_enc.c b/src/enc/analysis_enc.c
index 08f471f5..a47ff7d4 100644
--- a/src/enc/analysis_enc.c
+++ b/src/enc/analysis_enc.c
@@ -434,7 +434,9 @@ typedef struct {
 } SegmentJob;
 
 // main work call
-static int DoSegmentsJob(SegmentJob* const job, VP8EncIterator* const it) {
+static int DoSegmentsJob(void* arg1, void* arg2) {
+  SegmentJob* const job = (SegmentJob*)arg1;
+  VP8EncIterator* const it = (VP8EncIterator*)arg2;
   int ok = 1;
   if (!VP8IteratorIsDone(it)) {
     uint8_t tmp[32 + WEBP_ALIGN_CST];
@@ -462,7 +464,7 @@ static void InitSegmentJob(VP8Encoder* const enc, SegmentJob* const job,
   WebPGetWorkerInterface()->Init(&job->worker);
   job->worker.data1 = job;
   job->worker.data2 = &job->it;
-  job->worker.hook = (WebPWorkerHook)DoSegmentsJob;
+  job->worker.hook = DoSegmentsJob;
   VP8IteratorInit(enc, &job->it);
   VP8IteratorSetRow(&job->it, start_row);
   VP8IteratorSetCountDown(&job->it, (end_row - start_row) * enc->mb_w_);
diff --git a/src/enc/vp8l_enc.c b/src/enc/vp8l_enc.c
index aeb52f38..2b3f3486 100644
--- a/src/enc/vp8l_enc.c
+++ b/src/enc/vp8l_enc.c
@@ -1754,7 +1754,7 @@ WebPEncodingError VP8LEncodeStream(const WebPConfig* const config,
       worker_interface->Init(worker);
       worker->data1 = param;
       worker->data2 = NULL;
-      worker->hook = (WebPWorkerHook)EncodeStreamHook;
+      worker->hook = EncodeStreamHook;
     }
   }