diff --git a/ChangeLog b/ChangeLog
index 6a1be9892a..c8677e367d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -14,6 +14,8 @@ Bugfix
    * Fix leap year calculation in x509_date_is_valid() to ensure that invalid
      dates on leap years with 100 and 400 intervals are handled correctly. Found
      by Nicholas Wilson. #694
+   * Fix crash when calling mbedtls_ssl_cache_free() twice. Found by
+     MilenkoMitrovic, #1104
 
 = mbed TLS 1.3.21 branch released 2017-08-10
 
diff --git a/library/ssl_cache.c b/library/ssl_cache.c
index 0c2df29bb1..1cb71bf575 100644
--- a/library/ssl_cache.c
+++ b/library/ssl_cache.c
@@ -44,6 +44,12 @@
 #define polarssl_free       free
 #endif
 
+
+/* 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;
+}
+
 void ssl_cache_init( ssl_cache_context *cache )
 {
     memset( cache, 0, sizeof( ssl_cache_context ) );
@@ -324,6 +330,8 @@ void ssl_cache_free( ssl_cache_context *cache )
 #if defined(POLARSSL_THREADING_C)
     polarssl_mutex_free( &cache->mutex );
 #endif
+
+    polarssl_zeroize( cache, sizeof(ssl_cache_context) );
 }
 
 #endif /* POLARSSL_SSL_CACHE_C */