diff --git a/library/pkparse.c b/library/pkparse.c
index 6fb0dd5..5786db7 100644
--- a/library/pkparse.c
+++ b/library/pkparse.c
@@ -61,12 +61,15 @@
 #define polarssl_free       free
 #endif
 
-#if defined(POLARSSL_FS_IO)
+#if defined(POLARSSL_FS_IO) || \
+    defined(POLARSSL_PKCS12_C) || defined(POLARSSL_PKCS5_C)
 /* Implementation that should never be optimized out by the compiler */
 static void polarssl_zeroize( void *v, size_t n ) {
     volatile unsigned char *p = v; while( n-- ) *p++ = 0;
 }
+#endif
 
+#if defined(POLARSSL_FS_IO)
 /*
  * Load all data from a file into a given buffer.
  */