diff --git a/crypto/drbg.c b/crypto/drbg.c
index ff975d9..7894db9 100644
--- a/crypto/drbg.c
+++ b/crypto/drbg.c
@@ -1500,7 +1500,7 @@
 		if (0 >= tmplen)
 			return tmplen;
 		len += tmplen;
-	} while (slice > 0);
+	} while (slice > 0 && (len < buflen));
 	return len;
 }