diff --git a/tests/zstreamtest.c b/tests/zstreamtest.c
index 2c25adf3c..93032d21e 100644
--- a/tests/zstreamtest.c
+++ b/tests/zstreamtest.c
@@ -958,7 +958,7 @@ static int basicUnitTests(U32 seed, double compressibility, int bigTests)
                 break;
             out.size = MIN(out.size + cSize / 4, compressedBufferSize);
         }
-        CHECK_Z(ZSTD_decompress(decodedBuffer, CNBufferSize, compressedBuffer, cSize));
+        CHECK_Z(ZSTD_decompress(decodedBuffer, CNBufferSize, compressedBuffer, out.pos));
         DISPLAYLEVEL(3, "OK \n");
 
         DISPLAYLEVEL(3, "test%3i : ZSTD_compressStream2() ZSTD_c_stableInBuffer modify buffer : ", testNb++);