diff --git a/LongestCommonPrefix.h b/LongestCommonPrefix.h
index da3c824..5490f97 100644
--- a/LongestCommonPrefix.h
+++ b/LongestCommonPrefix.h
@@ -125,7 +125,7 @@ __attribute__((target("default")))
 inline int
 longestCommonPrefix(const uint8_t *ap, const uint8_t *bp, int cl) {
   if (!(cl >= 0)) {
-    __builtin_unreachable();
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
 
   int i = 0;