diff --git a/Makefile b/Makefile
index cbdb948..4bc6c3f 100644
--- a/Makefile
+++ b/Makefile
@@ -24,7 +24,8 @@ JS_PRE := $(wildcard javascript/*pre.js)
 JS_POST := $(wildcard javascript/*post.js)
 
 CPPFLAGS += -Iinclude -Ilib
-CFLAGS += -Wall -Werror -std=c89 -fPIC
+# we rely on <stdint.h>, which was introduced in C99
+CFLAGS += -Wall -Werror -std=c99 -fPIC
 CXXFLAGS += -Wall -Werror -std=c++11 -fPIC
 LDFLAGS += -Wall -Werror
 
diff --git a/src/libs.cpp b/src/libs.c
similarity index 95%
rename from src/libs.cpp
rename to src/libs.c
index 6757574..4304354 100644
--- a/src/libs.cpp
+++ b/src/libs.c
@@ -1,4 +1,4 @@
-/* Copyright 2015 OpenMarket Ltd
+/* Copyright 2015-6 OpenMarket Ltd
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -12,7 +12,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-extern "C" {
 #include "crypto-algorithms/sha256.c"
 #include "crypto-algorithms/aes.c"
 #include "curve25519-donna/curve25519-donna.c"
@@ -24,4 +23,3 @@ extern "C" {
 #include "ed25519/src/verify.c"
 #include "ed25519/src/sign.c"
 #include "ed25519_additions.c"
-}