diff --git a/libavutil/dict.c b/libavutil/dict.c
index 0d54c7970a..caec50eff7 100644
--- a/libavutil/dict.c
+++ b/libavutil/dict.c
@@ -107,7 +107,7 @@ int av_dict_set(AVDictionary **pm, const char *key, const char *value,
         if (flags & AV_DICT_DONT_STRDUP_VAL) {
             m->elems[m->count].value = (char*)(intptr_t)value;
         } else if (oldval && flags & AV_DICT_APPEND) {
-            int len = strlen(oldval) + strlen(value) + 1;
+            size_t len = strlen(oldval) + strlen(value) + 1;
             char *newval = av_mallocz(len);
             if (!newval)
                 goto err_out;