diff --git a/tests/scripts/key-exchanges.pl b/tests/scripts/key-exchanges.pl
index 9e35cfa44..46826c3de 100755
--- a/tests/scripts/key-exchanges.pl
+++ b/tests/scripts/key-exchanges.pl
@@ -35,7 +35,7 @@ for my $kex (@kexes) {
             and abort "Failed to disable $k\n";
     }
 
-    system( "make lib" ) and abort "Failed to build lib: $kex\n";
+    system( "make lib CFLAGS='-Os -Werror'" ) and abort "Failed to build lib: $kex\n";
 }
 
 system( "mv $config_h.bak $config_h" ) and die "$config_h not restored\n";
diff --git a/tests/scripts/test-ref-configs.pl b/tests/scripts/test-ref-configs.pl
index d1cc924bf..c3d1426eb 100755
--- a/tests/scripts/test-ref-configs.pl
+++ b/tests/scripts/test-ref-configs.pl
@@ -57,7 +57,7 @@ while( my ($conf, $args) = each %configs ) {
     system( "cp configs/$conf $config_h" )
         and abort "Failed to activate $conf\n";
 
-    system( "make" ) and abort "Failed to build: $conf\n";
+    system( "make CFLAGS='-Os -Werror'" ) and abort "Failed to build: $conf\n";
     system( "make test" ) and abort "Failed test suite: $conf\n";
 
     if( $args )