diff --git a/src/db.zig b/src/db.zig
index e28f40f..284a423 100644
--- a/src/db.zig
+++ b/src/db.zig
@@ -204,7 +204,6 @@ pub const DB = struct {
         const result = self.tree.get(key);
 
         if (result) |dataptr| {
-            // const entry = result.found;
             if (value.len == dataptr.size) {
                 return self._inplace_update(value, dataptr);
             }
@@ -294,6 +293,7 @@ pub const DB = struct {
         }
     }
 
+    /// Calling this function block the database completely.
     pub fn for_each(
         self: *DB,
         allocator: std.mem.Allocator,
@@ -301,6 +301,15 @@ pub const DB = struct {
         ctx_: T,
         fun: fn (T, []const u8, []const u8) anyerror!bool,
     ) !void {
+        try check_is_open(self);
+        if (!self.deinit_mut.tryLockShared()) {
+            return error.ClosedDB;
+        }
+        defer self.deinit_mut.unlockShared();
+
+        self.db_mut.lock();
+        defer self.db_mut.unlock();
+
         const ctx_t = struct {
             db: *DB,
             allocator: std.mem.Allocator,