diff --git a/core/string/ustring.cpp b/core/string/ustring.cpp
index daeb7fbd172..8728f4e4ead 100644
--- a/core/string/ustring.cpp
+++ b/core/string/ustring.cpp
@@ -2178,7 +2178,7 @@ int64_t String::bin_to_int() const {
 		s++;
 	}
 
-	if (len > 2 && s[0] == '0' && s[1] == 'b') {
+	if (len > 2 && s[0] == '0' && lower_case(s[1]) == 'b') {
 		s += 2;
 	}