diff --git a/tests/fuzzer.c b/tests/fuzzer.c
index b9d319ea..c411d417 100644
--- a/tests/fuzzer.c
+++ b/tests/fuzzer.c
@@ -414,7 +414,7 @@ static int basicUnitTests(U32 seed, double compressibility)
     DISPLAYLEVEL(3, "test%3d : re-using a CCtx should compress the same : ", testNb++);
     {   int i;
         for (i=0; i<20; i++)
-            ((char*)CNBuffer)[i] = i;   /* ensure no match during initial section */
+            ((char*)CNBuffer)[i] = (char)i;   /* ensure no match during initial section */
         memcpy((char*)CNBuffer + 20, CNBuffer, 10);   /* create one match, starting from beginning of sample, which is the difficult case (see #1241) */
         for (i=1; i<=19; i++) {
             ZSTD_CCtx* const cctx = ZSTD_createCCtx();