diff --git a/libavutil/mem.c b/libavutil/mem.c
index 10b0137a7e..e50df1ec41 100644
--- a/libavutil/mem.c
+++ b/libavutil/mem.c
@@ -258,7 +258,7 @@ 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);