diff --git a/programs/pkey/rsa_sign.c b/programs/pkey/rsa_sign.c
index 7bd0fad67..c9bdd3afe 100644
--- a/programs/pkey/rsa_sign.c
+++ b/programs/pkey/rsa_sign.c
@@ -141,7 +141,7 @@ int main( int argc, char *argv[] )
     /*
      * Write the signature into <filename>.sig
      */
-    snprintf( filename, sizeof( filename ), "%s.sig", argv[1] );
+    polarssl_snprintf( filename, sizeof( filename ), "%s.sig", argv[1] );
 
     if( ( f = fopen( filename, "wb+" ) ) == NULL )
     {
diff --git a/programs/pkey/rsa_verify.c b/programs/pkey/rsa_verify.c
index 325ae6a2e..4011df6a2 100644
--- a/programs/pkey/rsa_verify.c
+++ b/programs/pkey/rsa_verify.c
@@ -105,7 +105,7 @@ int main( int argc, char *argv[] )
      * Extract the RSA signature from the text file
      */
     ret = 1;
-    snprintf( filename, sizeof( filename ), "%s.sig", argv[1] );
+    polarssl_snprintf( filename, sizeof( filename ), "%s.sig", argv[1] );
 
     if( ( f = fopen( filename, "rb" ) ) == NULL )
     {