diff --git a/common/lfdemod.c b/common/lfdemod.c
index 27bef1dd2..f231cd69f 100644
--- a/common/lfdemod.c
+++ b/common/lfdemod.c
@@ -148,6 +148,9 @@ uint32_t bytebits_to_byteLSBF(uint8_t *src, size_t numbits)
 //search for given preamble in given BitStream and return success=1 or fail=0 and startIndex and length
 uint8_t preambleSearch(uint8_t *BitStream, uint8_t *preamble, size_t pLen, size_t *size, size_t *startIdx)
 {
+	// Sanity check.  If preamble length is bigger than bitstream length.
+	if ( *size <= pLen ) return 0;
+	
 	uint8_t foundCnt = 0;
 	for (int idx = 0; idx < *size - pLen; idx++){
 		if (memcmp(BitStream+idx, preamble, pLen) == 0){