diff --git a/tests/Makefile b/tests/Makefile
index a3365103..619bafe6 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -68,22 +68,25 @@ distclean: clean
 #####################################################################################################
 
 gene-list:
-	$(CC) $(CFLAGS) $(CPPFLAGS) -O3 -DNDEBUG -S tgen-mlist.c && less tgen-mlist.s
+	$(CC) $(CFLAGS) $(CPPFLAGS) -O3 -march=native -DNDEBUG -S tgen-mlist.c && less tgen-mlist.s
 
 gene-array:
-	$(CC) $(CFLAGS) $(CPPFLAGS) -O3 -DNDEBUG -S tgen-marray.c && less tgen-marray.s
+	$(CC) $(CFLAGS) $(CPPFLAGS) -O3 -march=native -DNDEBUG -S tgen-marray.c && less tgen-marray.s
 
 gene-shared:
-	$(CC) $(CFLAGS) $(CPPFLAGS) -O3 -DNDEBUG -S tgen-shared.c && less tgen-shared.s
+	$(CC) $(CFLAGS) $(CPPFLAGS) -O3 -march=native -DNDEBUG -S tgen-shared.c && less tgen-shared.s
 
 gene-bitset:
-	$(CC) $(CFLAGS) $(CPPFLAGS) -O3 -DNDEBUG -S tgen-bitset.c && less tgen-bitset.s
+	$(CC) $(CFLAGS) $(CPPFLAGS) -O3 -march=native -DNDEBUG -S tgen-bitset.c && less tgen-bitset.s
 
 gene-dict:
-	$(CC) $(CFLAGS) $(CPPFLAGS) -O3 -DNDEBUG -S tgen-mdict.c && less tgen-mdict.s
+	$(CC) $(CFLAGS) $(CPPFLAGS) -O3 -march=native -DNDEBUG -S tgen-mdict.c && less tgen-mdict.s
 
 gene-queue:
-	$(CC) $(CFLAGS) $(CPPFLAGS) -O3 -DNDEBUG -S tgen-queue.c && less tgen-queue.s
+	$(CC) $(CFLAGS) $(CPPFLAGS) -O3 -march=native -DNDEBUG -S tgen-queue.c && less tgen-queue.s
+
+gene-string:
+	$(CC) $(CFLAGS) $(CPPFLAGS) -O3 -march=native -DNDEBUG -S tgen-mstring.c && less tgen-mstring.s
 
 #####################################################################################################
 # Coverage
diff --git a/tests/tgen-mstring.c b/tests/tgen-mstring.c
new file mode 100644
index 00000000..b30655e3
--- /dev/null
+++ b/tests/tgen-mstring.c
@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2017-2018, Patrick Pelissier
+ * All rights reserved.
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * + Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * + Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE REGENTS AND CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+#include "m-string.h"
+
+size_t fsize(const char str[])
+{
+  return stringi_utf8_length(str);
+}