diff --git a/sharpyuv/sharpyuv.c b/sharpyuv/sharpyuv.c
index 3fc8496c..5ff02225 100644
--- a/sharpyuv/sharpyuv.c
+++ b/sharpyuv/sharpyuv.c
@@ -414,6 +414,22 @@ static int DoSharpArgbToYuv(const uint8_t* r_ptr, const uint8_t* g_ptr,
 }
 #undef SAFE_ALLOC
 
+#if defined(WEBP_USE_THREAD) && !defined(_WIN32)
+#include <pthread.h>  // NOLINT
+
+#define LOCK_ACCESS \
+    static pthread_mutex_t sharpyuv_lock = PTHREAD_MUTEX_INITIALIZER; \
+    if (pthread_mutex_lock(&sharpyuv_lock)) return
+#define UNLOCK_ACCESS_AND_RETURN                  \
+    do {                                          \
+      (void)pthread_mutex_unlock(&sharpyuv_lock); \
+      return;                                     \
+    } while (0)
+#else  // !(defined(WEBP_USE_THREAD) && !defined(_WIN32))
+#define LOCK_ACCESS do {} while (0)
+#define UNLOCK_ACCESS_AND_RETURN return
+#endif  // defined(WEBP_USE_THREAD) && !defined(_WIN32)
+
 // Hidden exported init function.
 // By default SharpYuvConvert calls it with NULL. If needed, users can declare
 // it as extern and call it with a VP8CPUInfo function.
@@ -421,17 +437,21 @@ SHARPYUV_EXTERN void SharpYuvInit(VP8CPUInfo cpu_info_func);
 void SharpYuvInit(VP8CPUInfo cpu_info_func) {
   static volatile VP8CPUInfo sharpyuv_last_cpuinfo_used =
       (VP8CPUInfo)&sharpyuv_last_cpuinfo_used;
-  const int initialized =
+  LOCK_ACCESS;
+  {
+    const int initialized =
       (sharpyuv_last_cpuinfo_used != (VP8CPUInfo)&sharpyuv_last_cpuinfo_used);
-  if (cpu_info_func == NULL && initialized) return;
-  if (sharpyuv_last_cpuinfo_used == cpu_info_func) return;
+    if (cpu_info_func == NULL && initialized) UNLOCK_ACCESS_AND_RETURN;
+    if (sharpyuv_last_cpuinfo_used == cpu_info_func) UNLOCK_ACCESS_AND_RETURN;
 
-  SharpYuvInitDsp(cpu_info_func);
-  if (!initialized) {
-    SharpYuvInitGammaTables();
+    SharpYuvInitDsp(cpu_info_func);
+    if (!initialized) {
+      SharpYuvInitGammaTables();
+    }
+
+    sharpyuv_last_cpuinfo_used = cpu_info_func;
   }
-
-  sharpyuv_last_cpuinfo_used = cpu_info_func;
+  UNLOCK_ACCESS_AND_RETURN;
 }
 
 int SharpYuvConvert(const void* r_ptr, const void* g_ptr,