diff --git a/os/backtrace.c b/os/backtrace.c
index a421140fb..dafb9904b 100644
--- a/os/backtrace.c
+++ b/os/backtrace.c
@@ -38,7 +38,7 @@
 void xorg_backtrace(void)
 {
     void *array[64];
-    char *mod;
+    const char *mod;
     int size, i;
     Dl_info info;
     ErrorF("\nBacktrace:\n");
@@ -48,10 +48,10 @@ void xorg_backtrace(void)
 	mod = (info.dli_fname && *info.dli_fname) ? info.dli_fname : "(vdso)";
 	if (info.dli_saddr)
 	    ErrorF("%d: %s (%s+0x%lx) [%p]\n", i, mod,
-		   info.dli_sname, array[i] - info.dli_saddr, array[i]);
+		   info.dli_sname, (char *) array[i] - (char *) info.dli_saddr, array[i]);
 	else
 	    ErrorF("%d: %s (%p+0x%lx) [%p]\n", i, mod,
-		   info.dli_fbase, array[i] - info.dli_fbase, array[i]);
+		   info.dli_fbase, (char *) array[i] - (char *) info.dli_fbase, array[i]);
     }
 }