diff --git a/default.nix b/default.nix
index 8b681a9..a33fad2 100644
--- a/default.nix
+++ b/default.nix
@@ -11,7 +11,7 @@ stdenv.mkDerivation {
   buildInputs = [ elmPackages.elm ninja nodePackages.uglify-js ];
   buildPhase = ''
     ./script/ninja.sh > build.ninja
-    env ELM_HOME=.elm ninja
+    env ELM_HOME=.elm ELM_FLAGS= ninja
   '';
 
   installPhase = "cp -r dist/ $out/";
diff --git a/modd.conf b/modd.conf
index 9b6a63d..a16daeb 100644
--- a/modd.conf
+++ b/modd.conf
@@ -1,9 +1,9 @@
 script/ninja.sh {
-    prep: ./script/ninja.sh > build.ninja && ninja
+    prep: ./script/ninja.sh > build.ninja && env ELM_FLAGS=--debug ninja
 }
 
 src/** vendor/** {
-    prep: ninja
+    prep: env ELM_FLAGS=--debug ninja
 }
 
 dist/** {
diff --git a/script/elm-make-module.sh b/script/elm-make-module.sh
index f03b875..e6ee10e 100755
--- a/script/elm-make-module.sh
+++ b/script/elm-make-module.sh
@@ -4,14 +4,14 @@ set -euo pipefail
 
 IN="${1:-}"
 OUT="${2:-}"
-FLAGS="${@:3}"
+ELM_FLAGS="${ELM_FLAGS:-}"
 
 if test -z "$IN" || test -z "$OUT"; then
     echo "usage: ${0:-} src/Main.elm dist/elm.js --optimize"
     exit 1
 fi
 
-elm make "$FLAGS" --output="$OUT" "$IN"
+elm make $ELM_FLAGS --output="$OUT" "$IN"
 
 # change the cmpiled elm file to not immediately call the compiled function
 sed -i 's/(function(scope/function init(scope/g' "$OUT"
diff --git a/script/ninja.sh b/script/ninja.sh
index b8d58b2..4982286 100755
--- a/script/ninja.sh
+++ b/script/ninja.sh
@@ -4,10 +4,8 @@ set -eou pipefail
 ELM_FILES="$(find src -name '*.elm')"
 
 cat <<EOF
-elmFlags=--debug
-
 rule elm
-  command = ./script/elm-make-module.sh \$in \$out \$elmFlags
+  command = ./script/elm-make-module.sh \$in \$out
 
 rule es6ify
   command = ./script/es6ify.sh \$in \$export > \$out