diff --git a/src/normalize.c b/src/normalize.c
index f8f241e3..4eeda0f9 100644
--- a/src/normalize.c
+++ b/src/normalize.c
@@ -10,10 +10,13 @@ char *normalize_string_utf8(char *str, uint64_t options) {
 
     bool have_utf8proc_options = false;
 
+    char *normalized = NULL;
+
     if (options & NORMALIZE_STRING_TRIM) {
         char *trimmed = string_trim(str);
         if (trimmed != NULL) {
-            str = trimmed;
+            normalized = trimmed;
+            str = normalized;
         }
     }
 
@@ -37,8 +40,6 @@ char *normalize_string_utf8(char *str, uint64_t options) {
         utf8proc_options |= UTF8PROC_OPTIONS_LOWERCASE;
     }
 
-    char *normalized = NULL;
-
     if (have_utf8proc_options) {
         utf8proc_map((uint8_t *)str, 0, &utf8proc_normalized, utf8proc_options);
 
@@ -46,9 +47,11 @@ char *normalize_string_utf8(char *str, uint64_t options) {
         str = normalized;
     }
 
-    if (options & NORMALIZE_STRING_REPLACE_HYPHENS) {
-        string_replace(str, '-', ' ');
-        normalized = str;
+    if (options & NORMALIZE_STRING_REPLACE_HYPHENS && strchr(str, '-') != NULL) {
+        char *replaced = string_replace(str, '-', ' ');
+        if (replaced != NULL) {
+            normalized = replaced;
+        }
     }
 
     return normalized;
diff --git a/src/string_utils.c b/src/string_utils.c
index 12f483bf..ce5ea30f 100644
--- a/src/string_utils.c
+++ b/src/string_utils.c
@@ -80,10 +80,14 @@ inline void string_upper(char *s) {
     for (; *s; ++s) *s = toupper(*s);
 }
 
-inline void string_replace(char *s, char c1, char c2) {
-    for (; *s; ++s) {
-        if (*s == c1) *s = c2;
+inline char *string_replace(char *s, char c1, char c2) {
+    char *repl = strdup(s);
+    if (repl == NULL) return NULL;
+    char *ptr = repl;
+    for (; *ptr; ++ptr) {
+        if (*ptr == c1) *ptr = c2;
     }
+    return repl;
 }
 
 inline bool string_is_upper(char *s) {
diff --git a/src/string_utils.h b/src/string_utils.h
index 2295316c..67a65e72 100644
--- a/src/string_utils.h
+++ b/src/string_utils.h
@@ -55,7 +55,7 @@ void string_lower(char *s);
 bool string_is_upper(char *s);
 void string_upper(char *s);
 
-void string_replace(char *s, char c1, char c2);
+char *string_replace(char *s, char c1, char c2);
 
 bool string_starts_with(const char *str, const char *start);
 bool string_ends_with(const char *str, const char *ending);