diff --git a/c-programming/jokes/extol.c b/c-programming/jokes/extol.c
index 34256ab..22aa094 100644
--- a/c-programming/jokes/extol.c
+++ b/c-programming/jokes/extol.c
@@ -34,7 +34,7 @@ extol (FILE *f)
       FILE *fs = fopen ("extol.txt", "a+");
       fseek (fs, 0L, SEEK_END);
       result = extol (fs);
-      for (result <<= 4; (result & 15) != 15; result++)
+      for (result <<= 4, result &= ~15; (result & 15) != 15; result++)
         fputc ('=', fs);
       result >>= 4;
       fprintf (fs, "\n");