diff --git a/src/resources.c b/src/resources.c
index 87c1a15..2629483 100644
--- a/src/resources.c
+++ b/src/resources.c
@@ -2,6 +2,7 @@
 #include <string.h>
 #include <stdio.h>
 #include <unistd.h>
+#include <ctype.h>
 
 #include "resources.h"
 #include "disasm.h"
@@ -98,7 +99,7 @@ int get_mnemonic_resource( char* name, char* class ) {
     if ( !s )
         return CLASS_MNEMONICS;
     for ( tmp = buf; *s; s++ )
-        *tmp++ = isupper( *s ) ? _tolower( *s ) : *s;
+        *tmp++ = isupper( *s ) ? tolower( *s ) : *s;
     *tmp = 0;
     free( os );
 
@@ -118,7 +119,7 @@ int get_boolean_resource( char* name, char* class ) {
     if ( !s )
         return 0;
     for ( tmp = buf; *s; s++ )
-        *tmp++ = isupper( *s ) ? _tolower( *s ) : *s;
+        *tmp++ = isupper( *s ) ? tolower( *s ) : *s;
     *tmp = 0;
     free( os );
 
@@ -225,7 +226,7 @@ Visual* get_visual_resource( Display* dpy, char* name, char* class,
     if ( s )
         for ( tmp = s; *tmp; tmp++ )
             if ( isupper( *tmp ) )
-                *tmp = _tolower( *tmp );
+                *tmp = tolower( *tmp );
 
     if ( !s || !strcmp( s, "default" ) )
         vclass = -1;
diff --git a/src/resources.h b/src/resources.h
index 8db4c6a..c503c19 100644
--- a/src/resources.h
+++ b/src/resources.h
@@ -47,23 +47,8 @@ extern Visual* get_visual_resource( Display* dpy, char* name, char* class,
                                     unsigned int* depth );
 extern XFontStruct* get_font_resource( Display* dpy, char* res_name,
                                        char* res_class );
-
-#ifndef isupper
-#define isupper( c ) ( ( c ) >= 'A' && ( c ) <= 'Z' )
-#endif
-#ifndef islower
-#define islower( c ) ( ( c ) >= 'a' && ( c ) <= 'z' )
-#endif
-#ifndef _tolower
-#define _tolower( c ) ( ( c ) - 'A' + 'a' )
-#endif
-#ifndef _toupper
-#define _toupper( c ) ( ( c ) - 'a' + 'A' )
-#endif
-#endif
-
-#if defined( GUI_IS_SDL1 )
-void get_resources( void );
+#elif defined( GUI_IS_SDL1 )
+extern void get_resources( void );
 #endif
 
 #endif /* !_RESOURCES_H */
diff --git a/src/x48.c b/src/x48.c
index 004ebff..f345b49 100644
--- a/src/x48.c
+++ b/src/x48.c
@@ -3,9 +3,10 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
+#include <ctype.h>
 #include <sys/stat.h>
 #include <sys/types.h>
-#include <unistd.h>
 #include <sys/utsname.h>
 
 #if defined( GUI_IS_X11 )
@@ -1380,7 +1381,7 @@ int InitDisplay( int argc, char** argv ) {
 
     res_name = progname;
     res_class = strdup( res_name );
-    *res_class = islower( *res_class ) ? _toupper( *res_class ) : *res_class;
+    *res_class = islower( *res_class ) ? toupper( *res_class ) : *res_class;
 
     /*
      * look for argument -name
@@ -1393,12 +1394,12 @@ int InitDisplay( int argc, char** argv ) {
         }
 
         for ( s = res_name; *s; s++ )
-            *s = isupper( *s ) ? _tolower( *s ) : *s;
+            *s = isupper( *s ) ? tolower( *s ) : *s;
 
         free( res_class );
         res_class = strdup( res_name );
         *res_class =
-            islower( *res_class ) ? _toupper( *res_class ) : *res_class;
+            islower( *res_class ) ? toupper( *res_class ) : *res_class;
 
         argc = saved_argc;
         argv = ( char** )malloc( ( argc + 1 ) * sizeof( char* ) );