diff --git a/libavfilter/formats.c b/libavfilter/formats.c
index c91f8b2cf8..39b3453e41 100644
--- a/libavfilter/formats.c
+++ b/libavfilter/formats.c
@@ -43,6 +43,9 @@ AVFilterFormats *avfilter_merge_formats(AVFilterFormats *a, AVFilterFormats *b)
     AVFilterFormats *ret;
     unsigned i, j, k = 0;
 
+    if (a == b)
+        return a;
+
     if (a == b)
         return a;