diff --git a/library/pkparse.c b/library/pkparse.c
index 2664fe9..9cad2cd 100644
--- a/library/pkparse.c
+++ b/library/pkparse.c
@@ -60,12 +60,15 @@
 #define mbedtls_free       free
 #endif
 
-#if defined(MBEDTLS_FS_IO)
+#if defined(MBEDTLS_FS_IO) || \
+    defined(MBEDTLS_PKCS12_C) || defined(MBEDTLS_PKCS5_C)
 /* Implementation that should never be optimized out by the compiler */
 static void mbedtls_zeroize( void *v, size_t n ) {
     volatile unsigned char *p = v; while( n-- ) *p++ = 0;
 }
+#endif
 
+#if defined(MBEDTLS_FS_IO)
 /*
  * Load all data from a file into a given buffer.
  *