diff --git a/programs/x509/crl_app.c b/programs/x509/crl_app.c
index fc22188..87793f7 100644
--- a/programs/x509/crl_app.c
+++ b/programs/x509/crl_app.c
@@ -72,6 +72,19 @@
     const char *filename;       /* filename of the certificate file     */
 } opt;
 
+#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
+int mbedtls_hardware_poll( void *data, unsigned char *output,
+                           size_t len, size_t *olen )
+{
+    size_t i;
+    (void) data;
+    for( i = 0; i < len; ++i )
+        output[i] = rand();
+    *olen = len;
+    return( 0 );
+}
+#endif
+
 int main( int argc, char *argv[] )
 {
     int ret = 1;