diff --git a/src/config_loader.c b/src/config_loader.c
index 4f4f943b..f3ccb6d4 100644
--- a/src/config_loader.c
+++ b/src/config_loader.c
@@ -56,14 +56,6 @@ bool config_loader_set_opt(char *section, char *opt, char *value)
 	}
 	options = cl.available_opts;
 
-	/* replace all '_' used in config options with '-' used in flags */
-	flag = strdup_or_die(opt);
-	for (unsigned int i = 0; flag[i]; i++) {
-		if (flag[i] == '_') {
-			flag[i] = '-';
-		}
-	}
-
 	/* options within a section are by default considered to be global */
 	if (section) {
 		lsection = str_tolower(section);
@@ -75,6 +67,9 @@ bool config_loader_set_opt(char *section, char *opt, char *value)
 		}
 	}
 
+	/* replace all '_' used in config options with '-' used in flags */
+	flag = str_subchar(opt, '_', '-');
+
 	/* search the option from within the available options */
 	while (options->name != NULL) {
 		if (strcmp(flag, options->name) == 0) {
diff --git a/src/lib/strings.c b/src/lib/strings.c
index 59bad77b..8b37293c 100644
--- a/src/lib/strings.c
+++ b/src/lib/strings.c
@@ -179,3 +179,15 @@ bool strtobool(const char *str)
 	free_string(&str_lower);
 	return ret;
 }
+
+char *str_subchar(const char *str, char c1, char c2)
+{
+	char *new = strdup_or_die(str);
+	for (unsigned int i = 0; new[i]; i++) {
+		if (new[i] == c1) {
+			new[i] = c2;
+		}
+	}
+
+	return new;
+}
diff --git a/src/lib/strings.h b/src/lib/strings.h
index 95d2c0d0..6e20c9fd 100644
--- a/src/lib/strings.h
+++ b/src/lib/strings.h
@@ -88,6 +88,15 @@ char *str_tolower(const char *str);
  */
 bool strtobool(const char *str);
 
+/**
+ * Returns a copy of str with all chars c1 replaced with c2.
+ *
+ * @param str The original string.
+ * @param c1 Character to look for.
+ * @param c2 The character to replace c1 to.
+ */
+char *str_subchar(const char *str, char c1, char c2);
+
 #ifdef __cplusplus
 }
 #endif