diff --git a/src/Dict.cc b/src/Dict.cc
index 47e350c98d..b438387375 100644
--- a/src/Dict.cc
+++ b/src/Dict.cc
@@ -1027,8 +1027,14 @@ int Dictionary::LookupIndex(const void* key, int key_size, detail::hash_t hash,
 		*insert_position = i;
 
 	if ( insert_distance )
+		{
 		*insert_distance = i - bucket;
 
+		if ( *insert_distance >= detail::TOO_FAR_TO_REACH )
+			reporter->FatalErrorWithCore("Dictionary (size %d) insertion distance too far: %d",
+			                             Length(), *insert_distance);
+		}
+
 	return -1;
 	}