diff --git a/mongoose.c b/mongoose.c
index 4b5603bd..cb5a10bd 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -236,7 +236,7 @@ enum cs_log_level {
 void cs_log_set_level(enum cs_log_level level);
 
 /* Set log filter. NULL (a default) logs everything. */
-void cs_log_set_filter(char *source_file_name);
+void cs_log_set_filter(const char *source_file_name);
 
 int cs_log_print_prefix(enum cs_log_level level, const char *func,
                         const char *filename);
@@ -316,8 +316,8 @@ double cs_log_ts WEAK;
 
 enum cs_log_level cs_log_cur_msg_level WEAK = LL_NONE;
 
-void cs_log_set_filter(char *str) WEAK;
-void cs_log_set_filter(char *str) {
+void cs_log_set_filter(const char *str) WEAK;
+void cs_log_set_filter(const char *str) {
   free(s_filter_pattern);
   if (str != NULL) {
     s_filter_pattern = strdup(str);