diff --git a/c/Makefile b/c/Makefile
index 9d63979..24e848e 100644
--- a/c/Makefile
+++ b/c/Makefile
@@ -88,7 +88,11 @@ CUDA_HOME ?= /usr/local/cuda
 NVCC      ?= $(CUDA_HOME)/bin/nvcc
 CUDA_ARCH ?= native
 NVCCFLAGS ?= -O3 -std=c++17 -arch=$(CUDA_ARCH) -Xcompiler=-Wall,-Wextra
+ifeq ($(IS_WIN),)
 PYTHON    ?= python3
+else
+PYTHON    ?= python
+endif
 CUDA_OBJ  =
 TEST_BINS = tests/test_json$(EXE) tests/test_st$(EXE) tests/test_tier$(EXE) tests/test_grammar$(EXE) tests/test_decode_batch$(EXE) tests/test_idot$(EXE) tests/test_i4_acc512$(EXE)
 
@@ -205,7 +209,7 @@ tests/test_i4_acc512$(EXE): tests/test_i4_acc512.c
 	$(CC) $(CFLAGS) $< -o $@ $(LDFLAGS)
 
 test-c: $(TEST_BINS)
-	@for test in $(TEST_BINS); do ./$$test || exit 1; done
+	$(PYTHON) tools/run_tests.py $(TEST_BINS)
 
 test-python:
 	$(PYTHON) -m unittest discover -s tests -p 'test_*.py'
@@ -219,7 +223,6 @@ check:
 	$(MAKE) test
 
 clean:
-	rm -f olmoe$(EXE) glm$(EXE) iobench$(EXE) backend_cuda.o backend_loader.o backend_cuda_test$(EXE) backend_cuda_bench$(EXE) backend_metal.o backend_metal_test coli_cuda.dll coli_cuda.lib coli_cuda.exp $(TEST_BINS)
-	rm -rf tests/__pycache__
+	$(PYTHON) tools/clean.py
 
 .PHONY: all glm cuda-test cuda-bench cuda-dll portable test-c test-python test check clean
diff --git a/c/tools/clean.py b/c/tools/clean.py
new file mode 100644
index 0000000..463618f
--- /dev/null
+++ b/c/tools/clean.py
@@ -0,0 +1,41 @@
+#!/usr/bin/env python3
+"""Remove build artifacts. Used by `make clean` so it works from any shell.
+
+Works from cmd.exe, PowerShell, Git Bash, or MSYS2 — no `rm` or POSIX
+`for` loop required. Silently ignores files that don't exist.
+"""
+import glob
+import os
+import shutil
+
+# Files (relative to c/) to remove if present.
+FILES = [
+    "olmoe", "olmoe.exe",
+    "glm", "glm.exe",
+    "iobench", "iobench.exe",
+    "backend_cuda.o", "backend_loader.o",
+    "backend_cuda_test", "backend_cuda_test.exe",
+    "backend_cuda_bench", "backend_cuda_bench.exe",
+    "backend_metal.o", "backend_metal_test",
+    "coli_cuda.dll", "coli_cuda.lib", "coli_cuda.exp",
+]
+# Test binaries match this pattern. Only remove executables (.exe on Windows,
+# no extension on Unix) — never .c or .py source files.
+TEST_GLOBS = ["tests/test_*.exe"]
+# Directories to remove.
+DIRS = ["tests/__pycache__"]
+
+removed = 0
+for f in FILES:
+    if os.path.exists(f):
+        os.remove(f)
+        removed += 1
+for pattern in TEST_GLOBS:
+    for f in glob.glob(pattern):
+        os.remove(f)
+        removed += 1
+for d in DIRS:
+    if os.path.isdir(d):
+        shutil.rmtree(d)
+        removed += 1
+print(f"clean: removed {removed} files/dirs")
diff --git a/c/tools/run_tests.py b/c/tools/run_tests.py
new file mode 100644
index 0000000..e2c17ac
--- /dev/null
+++ b/c/tools/run_tests.py
@@ -0,0 +1,19 @@
+#!/usr/bin/env python3
+"""Run C test binaries, exiting non-zero on the first failure.
+
+Used by `make test-c` so the test runner works from any shell (cmd.exe,
+PowerShell, Git Bash, MSYS2) without a POSIX `for` loop. Each test binary
+is a positional argument.
+"""
+import subprocess
+import sys
+
+failed = []
+for binary in sys.argv[1:]:
+    rc = subprocess.call([binary])
+    if rc != 0:
+        failed.append(binary)
+if failed:
+    for f in failed:
+        print(f"FAILED: {f}", file=sys.stderr)
+    sys.exit(1)