diff --git a/src/Protocol.zig b/src/Protocol.zig
index 4ffc6ec..83dedca 100644
--- a/src/Protocol.zig
+++ b/src/Protocol.zig
@@ -28,6 +28,7 @@ pub const Error = error{
     NotFound,
     ValueTooLarge,
     Exists,
+    InvalidKey,
 } || std.Io.Reader.Error || std.Io.Reader.DelimiterError || std.Io.Writer.Error;
 
 /// Returns true if the error is a protocol-level error where the connection
@@ -38,6 +39,7 @@ pub fn isResumable(err: anyerror) bool {
         error.NotFound,
         error.Exists,
         error.ValueTooLarge,
+        error.InvalidKey,
         => true,
         else => false,
     };
@@ -67,7 +69,15 @@ pub const SetMode = enum {
     prepend,
 };
 
+fn validateKey(key: []const u8) Error!void {
+    if (key.len == 0 or key.len > 250) return error.InvalidKey;
+    for (key) |c| {
+        if (c <= ' ' or c == 0x7f) return error.InvalidKey;
+    }
+}
+
 pub fn get(self: Protocol, key: []const u8, buf: []u8, opts: GetOpts) Error!?Info {
+    try validateKey(key);
     // Build command: mg <key> v f c [T<ttl>]
     try self.writer.print("mg {s} v f c", .{key});
     if (opts.ttl) |ttl| {
@@ -100,6 +110,7 @@ pub fn get(self: Protocol, key: []const u8, buf: []u8, opts: GetOpts) Error!?Inf
 // --- Set ---
 
 pub fn set(self: Protocol, key: []const u8, value: []const u8, opts: SetOpts, mode: SetMode) Error!void {
+    try validateKey(key);
     // Build command: ms <key> <size> [flags]
     try self.writer.print("ms {s} {d}", .{ key, value.len });
 
@@ -145,6 +156,7 @@ pub fn set(self: Protocol, key: []const u8, value: []const u8, opts: SetOpts, mo
 // --- Delete ---
 
 pub fn delete(self: Protocol, key: []const u8) Error!void {
+    try validateKey(key);
     try self.writer.print("md {s}\r\n", .{key});
     try self.writer.flush();
 
@@ -169,6 +181,7 @@ pub fn decr(self: Protocol, key: []const u8, delta: u64) Error!u64 {
 }
 
 fn arithmetic(self: Protocol, key: []const u8, delta: u64, is_decr: bool) Error!u64 {
+    try validateKey(key);
     // ma <key> v D<delta> [MD]
     try self.writer.print("ma {s} v D{d}", .{ key, delta });
     if (is_decr) {
@@ -197,6 +210,7 @@ fn arithmetic(self: Protocol, key: []const u8, delta: u64, is_decr: bool) Error!
 // --- Touch ---
 
 pub fn touch(self: Protocol, key: []const u8, ttl: u32) Error!void {
+    try validateKey(key);
     try self.writer.print("mg {s} T{d}\r\n", .{ key, ttl });
     try self.writer.flush();
 
@@ -355,3 +369,18 @@ test "parseResponse EX" {
     const resp = try parseResponse("EX");
     try std.testing.expectEqual(Response.exists, resp);
 }
+
+test "validateKey" {
+    try validateKey("valid_key");
+    try validateKey("a");
+    try validateKey("x" ** 250);
+
+    try std.testing.expectError(error.InvalidKey, validateKey(""));
+    try std.testing.expectError(error.InvalidKey, validateKey("x" ** 251));
+    try std.testing.expectError(error.InvalidKey, validateKey("has space"));
+    try std.testing.expectError(error.InvalidKey, validateKey("has\ttab"));
+    try std.testing.expectError(error.InvalidKey, validateKey("has\nnewline"));
+    try std.testing.expectError(error.InvalidKey, validateKey("has\r\nreturn"));
+    try std.testing.expectError(error.InvalidKey, validateKey("has\x00null"));
+    try std.testing.expectError(error.InvalidKey, validateKey("has\x7fdelete"));
+}