diff --git a/core/file.c b/core/file.c
index 8978c0e5..6786a3f9 100644
--- a/core/file.c
+++ b/core/file.c
@@ -260,3 +260,10 @@ int file_writef(struct file *file, const char *fmt, ...)
 		REPORT_ERRNO(file->f_name);
 	return ret;
 }
+
+int cache_file_write(struct cache_file *file, const void *data, size_t len)
+{
+	if (fwrite(data, len, 1, file->cf_file) == 1)
+		return len;
+	return -1;
+}
diff --git a/include/core/file.h b/include/core/file.h
index ad10d297..c9a9976e 100644
--- a/include/core/file.h
+++ b/include/core/file.h
@@ -135,4 +135,10 @@ int file_readf(struct file *, const char *, ...);
  */
 int file_writef(struct file *, const char *, ...);
 
+/*
+ * Write binary data to a cache file similar to fwrite(3).
+ * Returns the number of bytes successfully written.
+ */
+int cache_file_write(struct cache_file *, const void *, size_t);
+
 #endif /* OCARINA_CORE_FILE_H */
diff --git a/tests/core/file.c b/tests/core/file.c
index 6d172f78..648c9678 100644
--- a/tests/core/file.c
+++ b/tests/core/file.c
@@ -166,6 +166,7 @@ static void test_cache()
 	test_equal(cache_file_open(&file, OPEN_WRITE), (bool)false);
 
 	test_equal(cache_file_exists(&file), (bool)false);
+	test_equal(cache_file_write(&file, "abcde", 5), 5);
 	cache_file_close(&file);
 	test_equal((void *)file.cf_file, NULL);
 	test_equal(cache_file_exists(&file), (bool)true);