diff --git a/doc/site/core/map.markdown b/doc/site/core/map.markdown
index 189f58b2..a70e3f49 100644
--- a/doc/site/core/map.markdown
+++ b/doc/site/core/map.markdown
@@ -5,7 +5,11 @@ An associative collection that maps keys to values. More details [here](../maps.
 
 ### **clear**
 
-Removes all entries
+Removes all entries from the map.
+
+### **containsKey**(key)
+
+Returns `true` if the map contains `key` or `false` otherwise.
 
 ### **count**
 
diff --git a/src/wren_core.c b/src/wren_core.c
index fe06e07b..a6bca4a2 100644
--- a/src/wren_core.c
+++ b/src/wren_core.c
@@ -230,6 +230,21 @@ static int validateIndexValue(WrenVM* vm, Value* args, int count, double value,
   return -1;
 }
 
+// Validates that [key] is a valid object for use as a map key. Returns true if
+// it is. If not, reports an error and returns false.
+static bool validateKey(WrenVM* vm, Value* args, int index)
+{
+  Value arg = args[index];
+  if (IS_BOOL(arg) || IS_CLASS(arg) || IS_NULL(arg) ||
+      IS_NUM(arg) || IS_RANGE(arg) || IS_STRING(arg))
+  {
+    return true;
+  }
+
+  args[0] = OBJ_VAL(wrenNewString(vm, "Key must be a value type.", 25));
+  return false;
+}
+
 // Validates that the argument at [argIndex] is an integer within `[0, count)`.
 // Also allows negative indices which map backwards from the end. Returns the
 // valid positive index value. If invalid, reports an error and returns -1.
@@ -719,13 +734,19 @@ DEF_NATIVE(map_instantiate)
 
 DEF_NATIVE(map_subscript)
 {
-  // TODO: Validate key type.
-  RETURN_VAL(wrenMapGet(AS_MAP(args[0]), args[1]));
+  if (!validateKey(vm, args, 1)) return PRIM_ERROR;
+
+  Value value;
+  if (wrenMapGet(AS_MAP(args[0]), args[1], &value)) RETURN_VAL(value);
+
+  // Not found.
+  RETURN_NULL;
 }
 
 DEF_NATIVE(map_subscriptSetter)
 {
-  // TODO: Validate key type.
+  if (!validateKey(vm, args, 1)) return PRIM_ERROR;
+
   wrenMapSet(vm, AS_MAP(args[0]), args[1], args[2]);
   RETURN_VAL(args[2]);
 }
@@ -740,6 +761,14 @@ DEF_NATIVE(map_clear)
   RETURN_NULL;
 }
 
+DEF_NATIVE(map_containsKey)
+{
+  if (!validateKey(vm, args, 1)) return PRIM_ERROR;
+
+  Value dummy;
+  RETURN_BOOL(wrenMapGet(AS_MAP(args[0]), args[1], &dummy));
+}
+
 DEF_NATIVE(map_count)
 {
   RETURN_NUM(AS_MAP(args[0])->count);
@@ -1468,6 +1497,7 @@ void wrenInitializeCore(WrenVM* vm)
   NATIVE(vm->mapClass, "[ ]", map_subscript);
   NATIVE(vm->mapClass, "[ ]=", map_subscriptSetter);
   NATIVE(vm->mapClass, "clear", map_clear);
+  NATIVE(vm->mapClass, "containsKey ", map_containsKey);
   NATIVE(vm->mapClass, "count", map_count);
   NATIVE(vm->mapClass, "iterate_ ", map_iterate);
   NATIVE(vm->mapClass, "keyIteratorValue_ ", map_keyIteratorValue);
diff --git a/src/wren_value.c b/src/wren_value.c
index 060d3d9a..ea3bd883 100644
--- a/src/wren_value.c
+++ b/src/wren_value.c
@@ -489,7 +489,7 @@ static void ensureMapCapacity(WrenVM* vm, ObjMap* map)
   map->capacity = newCapacity;
 }
 
-Value wrenMapGet(ObjMap* map, Value key)
+bool wrenMapGet(ObjMap* map, Value key, Value* value)
 {
   // Figure out where to insert it in the table. Use open addressing and
   // basic linear probing.
@@ -502,10 +502,14 @@ Value wrenMapGet(ObjMap* map, Value key)
     MapEntry* entry = &map->entries[index];
 
     // If we found an empty slot, the key is not in the table.
-    if (IS_UNDEFINED(entry->key)) return NULL_VAL;
+    if (IS_UNDEFINED(entry->key)) return false;
 
     // If the key matches, we found it.
-    if (wrenValuesEqual(entry->key, key)) return entry->value;
+    if (wrenValuesEqual(entry->key, key))
+    {
+      *value = entry->value;
+      return true;
+    }
 
     // Try the next slot.
     index = (index + 1) % map->capacity;
diff --git a/src/wren_value.h b/src/wren_value.h
index 0745206b..137e65c6 100644
--- a/src/wren_value.h
+++ b/src/wren_value.h
@@ -638,13 +638,16 @@ Value wrenListRemoveAt(WrenVM* vm, ObjList* list, int index);
 // Creates a new empty map.
 ObjMap* wrenNewMap(WrenVM* vm);
 
-// Returns the value in [map] associated with [key] or `NULL_VALUE` if it wasn't
-// found.
-Value wrenMapGet(ObjMap* map, Value key);
+// Looks up [key] in [map]. If found, stores its value in [value] and returns
+// `true`. Otherwise, returns `false`.
+bool wrenMapGet(ObjMap* map, Value key, Value* value);
 
 // Associates [key] with [value] in [map].
 void wrenMapSet(WrenVM* vm, ObjMap* map, Value key, Value value);
 
+// Returns `true` if [map] contains [key].
+bool wrenMapContainsKey(WrenVM* vm, ObjMap* map, Value key);
+
 // Creates a new range from [from] to [to].
 Value wrenNewRange(WrenVM* vm, double from, double to, bool isInclusive);
 
diff --git a/test/map/contains_key.wren b/test/map/contains_key.wren
new file mode 100644
index 00000000..9dc97c23
--- /dev/null
+++ b/test/map/contains_key.wren
@@ -0,0 +1,11 @@
+var map = {
+  "one": 1,
+  "two": 2,
+  "three": 3
+}
+
+IO.print(map.containsKey("one")) // expect: true
+IO.print(map.containsKey("two")) // expect: true
+IO.print(map.containsKey("three")) // expect: true
+IO.print(map.containsKey("four")) // expect: false
+IO.print(map.containsKey("five")) // expect: false
diff --git a/test/map/contains_key_not_value.wren b/test/map/contains_key_not_value.wren
new file mode 100644
index 00000000..0477be74
--- /dev/null
+++ b/test/map/contains_key_not_value.wren
@@ -0,0 +1 @@
+var result = {}.containsKey([]) // expect runtime error: Key must be a value type.
diff --git a/test/map/subscript_key_not_value.wren b/test/map/subscript_key_not_value.wren
new file mode 100644
index 00000000..8e813e01
--- /dev/null
+++ b/test/map/subscript_key_not_value.wren
@@ -0,0 +1 @@
+var result = {}[[]] // expect runtime error: Key must be a value type.
diff --git a/test/map/subscript_setter_key_not_value.wren b/test/map/subscript_setter_key_not_value.wren
new file mode 100644
index 00000000..c8ec79b1
--- /dev/null
+++ b/test/map/subscript_setter_key_not_value.wren
@@ -0,0 +1 @@
+var result = {}[[]] = "value" // expect runtime error: Key must be a value type.