diff --git a/libavutil/mem.c b/libavutil/mem.c
index 35a82e8a2d..9dc1ac7a49 100644
--- a/libavutil/mem.c
+++ b/libavutil/mem.c
@@ -259,7 +259,7 @@ char *av_strdup(const char *s)
 {
     char *ptr = NULL;
     if (s) {
-        int len = strlen(s) + 1;
+        size_t len = strlen(s) + 1;
         ptr = av_realloc(NULL, len);
         if (ptr)
             memcpy(ptr, s, len);