diff --git a/ChangeLog.d/fix_zeroization.txt b/ChangeLog.d/fix_zeroization.txt
new file mode 100644
index 0000000000..ad74d9c59f
--- /dev/null
+++ b/ChangeLog.d/fix_zeroization.txt
@@ -0,0 +1,3 @@
+Bugfix
+   * Fix possible crash in TLS PRF code, if a failure to allocate memory occurs.
+     Reported by Michael Madsen in #6516.
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index a49f774ed1..3c91b45139 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -5635,7 +5635,9 @@ static int tls_prf_generic( mbedtls_md_type_t md_type,
 exit:
     mbedtls_md_free( &md_ctx );
 
-    mbedtls_platform_zeroize( tmp, tmp_len );
+    if ( tmp != NULL )
+        mbedtls_platform_zeroize( tmp, tmp_len );
+
     mbedtls_platform_zeroize( h_i, sizeof( h_i ) );
 
     mbedtls_free( tmp );