diff --git a/internal/code-generator/generator/heuristics.go b/internal/code-generator/generator/heuristics.go
index 67a9c0c..a49ad87 100644
--- a/internal/code-generator/generator/heuristics.go
+++ b/internal/code-generator/generator/heuristics.go
@@ -160,11 +160,12 @@ func parseYaml(file string) (*Heuristics, error) {
 
 // isUnsupportedRegexpSyntax filters regexp syntax that is not supported by RE2.
 // In particular, we stumbled up on usage of next cases:
+// - lookbehind & lookahead
 // - named & numbered capturing group/after text matching
 // - backreference
 // For referece on supported syntax see https://github.com/google/re2/wiki/Syntax
 func isUnsupportedRegexpSyntax(reg string) bool {
-	return strings.Contains(reg, `(?<`) || strings.Contains(reg, `\1`) ||
+	return strings.Contains(reg, `(?<`) || strings.Contains(reg, `(?=`) || strings.Contains(reg, `\1`) ||
 		// See https://github.com/github/linguist/pull/4243#discussion_r246105067
 		(strings.HasPrefix(reg, multilinePrefix+`/`) && strings.HasSuffix(reg, `/`))
 }