diff --git a/Source/winchar.cpp b/Source/winchar.cpp
index ee6de346..87d446be 100644
--- a/Source/winchar.cpp
+++ b/Source/winchar.cpp
@@ -82,7 +82,7 @@ WCHAR *winchar_strncpy(WCHAR *ws1, const WCHAR *ws2, size_t n)
   return ret;
 }
 
-size_t winchar_strlen(WCHAR *ws)
+size_t winchar_strlen(const WCHAR *ws)
 {
   size_t len = 0;
 
@@ -94,7 +94,7 @@ size_t winchar_strlen(WCHAR *ws)
   return len;
 }
 
-WCHAR *winchar_strdup(WCHAR *ws)
+WCHAR *winchar_strdup(const WCHAR *ws)
 {
   WCHAR *dup = new WCHAR[winchar_strlen(ws) + 1];
   winchar_strcpy(dup, ws);
diff --git a/Source/winchar.h b/Source/winchar.h
index a348e21c..07ac7e70 100644
--- a/Source/winchar.h
+++ b/Source/winchar.h
@@ -20,7 +20,7 @@ WCHAR *winchar_fromansi(const char* s, unsigned int codepage = CP_ACP);
 char *winchar_toansi(const WCHAR* ws, unsigned int codepage = CP_ACP);
 WCHAR *winchar_strcpy(WCHAR *ws1, const WCHAR *ws2);
 WCHAR *winchar_strncpy(WCHAR *ws1, const WCHAR *ws2, size_t n);
-size_t winchar_strlen(WCHAR *ws);
-WCHAR *winchar_strdup(WCHAR *ws);
+size_t winchar_strlen(const WCHAR *ws);
+WCHAR *winchar_strdup(const WCHAR *ws);
 int winchar_strcmp(const WCHAR *ws1, const WCHAR *ws2);
 int winchar_stoi(const WCHAR *ws);