diff --git a/.github/workflows/check_indentation.yml b/.github/workflows/check_indentation.yml
new file mode 100644
index 0000000..b4f089f
--- /dev/null
+++ b/.github/workflows/check_indentation.yml
@@ -0,0 +1,18 @@
+name: Check indentation
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Check tabs
+      run: make test_tabs
diff --git a/Makefile b/Makefile
index 90fd8a5..d3c932d 100644
--- a/Makefile
+++ b/Makefile
@@ -4,9 +4,9 @@ build: \
 
 ARCH := $(shell uname -m)
 
-MAIN_RS_SRCS := $(shell find src -type f -regex '^.*\.rs$$') Cargo.toml \
-	client/dst/index.html client/dst/script.js client/dst/style.css \
-	config.json
+FILES_RS := $(shell find src -type f -regex '^.*\.rs$$')
+FILES_CLIENT := client/dst/index.html client/dst/script.js client/dst/style.css
+MAIN_RS_SRCS := $(FILES_RS) $(FILES_CLIENT) Cargo.toml config.json
 
 SEARCH_REPLACE := lib/search_and_replace/target/release/search_and_replace
 
@@ -27,6 +27,17 @@ test: target/debug/zmp24
 	BIND_TO="$(DEV_BIND)" \
 	cargo test
 
+.PHONY: test_tabs
+test_tabs:
+	@for file in $(FILES_RS); do \
+		echo -n "$$file ... "; \
+		if grep -Eq '^\s*	' "$$file"; then \
+			echo "fail"; \
+			exit 1; \
+		fi; \
+		echo "ok"; \
+	done
+
 .PHONY: clean
 clean: client_clean
 	cargo clean