diff --git a/programs/pkey/pk_sign.c b/programs/pkey/pk_sign.c
index 0d02935..ada29f2 100644
--- a/programs/pkey/pk_sign.c
+++ b/programs/pkey/pk_sign.c
@@ -29,6 +29,7 @@
 #if defined(POLARSSL_PLATFORM_C)
 #include "polarssl/platform.h"
 #else
+#define polarssl_snprintf   snprintf
 #define polarssl_printf     printf
 #endif
 
@@ -133,7 +134,7 @@
     /*
      * Write the signature into <filename>-sig.txt
      */
-    snprintf( filename, sizeof(filename), "%s.sig", argv[2] );
+    polarssl_snprintf( filename, sizeof(filename), "%s.sig", argv[2] );
 
     if( ( f = fopen( filename, "wb+" ) ) == NULL )
     {