diff --git a/pkgs/development/tools/misc/gengetopt/default.nix b/pkgs/development/tools/misc/gengetopt/default.nix
index d24d4b66d66c..6420d56bba2f 100644
--- a/pkgs/development/tools/misc/gengetopt/default.nix
+++ b/pkgs/development/tools/misc/gengetopt/default.nix
@@ -27,6 +27,10 @@ stdenv.mkDerivation rec {
       'set +o posix'
   '';
 
+  env = lib.optionalAttrs stdenv.cc.isClang {
+    CXXFLAGS = "-std=c++14";
+  };
+
   meta = {
     description = "Command-line option parser generator";
 
diff --git a/pkgs/tools/misc/mmv/default.nix b/pkgs/tools/misc/mmv/default.nix
index b396de5002d9..c8ce33207787 100644
--- a/pkgs/tools/misc/mmv/default.nix
+++ b/pkgs/tools/misc/mmv/default.nix
@@ -20,6 +20,13 @@ stdenv.mkDerivation rec {
   nativeBuildInputs = [ gengetopt m4 git gnupg perl autoconf automake help2man pkg-config ];
   buildInputs = [ boehmgc ];
 
+  env = lib.optionalAttrs stdenv.cc.isClang {
+    NIX_CFLAGS_COMPILE = toString [
+      "-Wno-error=implicit-function-declaration"
+      "-Wno-error=implicit-int"
+    ];
+  };
+
   meta = {
     homepage = "https://github.com/rrthomas/mmv";
     description = "Utility for wildcard renaming, copying, etc";