diff --git a/Makefile b/Makefile
index ad2486f..5992bbd 100644
--- a/Makefile
+++ b/Makefile
@@ -60,7 +60,7 @@ test: $(BUILD_DIR)parigp.tmLanguage.json
 	 --grammar $(BUILD_DIR)parigp.tmLanguage.json \
 	 $(TEST_CASES)
 
-$(BUILD_DIR)gp_commands.tsv:
+$(BUILD_DIR)gp_commands.tsv: $(BUILD_DIR)
 	$(eval FUNCS := $(shell echo '\c' | gp -fq | grep -v 'RETURN'))
 	@printf 'Command\tType\n' > $@
 	@echo $(FUNCS) |\
@@ -84,13 +84,13 @@ define get_gp_list
 	 xargs -I@ $(SHELL) -c 'echo -e \@"\n"' | xargs $(4) >> $@
 endef
 
-$(BUILD_DIR)gp_member_functions.tsv:
+$(BUILD_DIR)gp_member_functions.tsv: $(BUILD_DIR)
 	$(call get_gp_list,'Member','?.',,-n1)
 
-$(BUILD_DIR)gp_types.tsv:
+$(BUILD_DIR)gp_types.tsv: $(BUILD_DIR)
 	$(call get_gp_list,'Type','\\t',tail -n+2 |,-n1)
 
-$(BUILD_DIR)gp_support_commands.tsv:
+$(BUILD_DIR)gp_support_commands.tsv: $(BUILD_DIR)
 	$(call get_gp_list,'MetaCommand','?\\',tail -n+4 | cut -d'{' -f1 | cut -d' ' -f1 |,-I@ echo '\@')
 
 GP_ITEMS := commands member_functions types support_commands
diff --git a/flake.nix b/flake.nix
index b47fce8..4c79ee1 100644
--- a/flake.nix
+++ b/flake.nix
@@ -39,6 +39,7 @@
                 yq-go
                 gnumake
                 gnused
+
                 python39
                 jinja2-cli
 
@@ -47,6 +48,7 @@
                 vscode_tmgrammar_test
               ];
               src = self;
+              configurePhase = "make clean";
               buildPhase = "make build";
               checkPhase = "make test";
               installPhase = "mkdir -p $out; cp syntaxes/* $out/";
diff --git a/scripts/compile-grammar.sh b/scripts/compile-grammar.sh
index 5b2b7b8..8c9f367 100755
--- a/scripts/compile-grammar.sh
+++ b/scripts/compile-grammar.sh
@@ -3,7 +3,6 @@
 # compile-grammar.sh - Builds TextMate grammar with help of Nix.
 
 # shellcheck shell=sh
-set -e
 
 
 scriptPath=$(readlink -f "$0")
@@ -12,7 +11,15 @@ rootDir=$(dirname "${scriptPath%/*}")
 statix check
 nix flake check --impure "$rootDir"
 
-cp "$(nix build --impure \
-                --no-link \
-                --print-out-paths "$rootDir")"/parigp* "$rootDir/syntaxes/"
-nix develop --check --impure "$rootDir"
+outDir="$(nix build --impure \
+                    --no-link \
+                    --print-build-logs \
+                    --print-out-paths "$rootDir")"
+cp "$outDir"/parigp* "$rootDir/syntaxes/"
+
+output=$(nix develop --check --impure "$rootDir")
+echo "$output"
+output=$(echo "$output" | grep '✖.*failed')
+if [ -n "$output" ]; then
+    exit 1
+fi