diff --git a/releasenotes.md b/releasenotes.md
index fae886856..5236e213c 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -47,6 +47,7 @@
 - Miscompilation: global struct with vector could generate an incorrect initializer.
 - `String.tokenize_all` would yield one too many empty tokens at the end.
 - `String.replace` no longer depends on `String.split`.
+- Fix the case where `\u<unicode char>` could crash the compiler on some platforms.
 
 ### Stdlib changes
 - Add `ThreadPool` join function to wait for all threads to finish in the pool without destroying the threads.
diff --git a/src/utils/lib.h b/src/utils/lib.h
index d49203041..c16df6afb 100644
--- a/src/utils/lib.h
+++ b/src/utils/lib.h
@@ -609,7 +609,7 @@ static char hex_conv[256] = {
 
 static inline int char_hex_to_nibble(char c)
 {
-	return hex_conv[(unsigned)c] - 1;
+	return hex_conv[(unsigned char)c] - 1;
 }
 
 static inline bool char_is_hex_or_(char c)