diff --git a/Userland/Libraries/LibJS/Runtime/ErrorTypes.h b/Userland/Libraries/LibJS/Runtime/ErrorTypes.h
index 9a203b365b..b1da75690d 100644
--- a/Userland/Libraries/LibJS/Runtime/ErrorTypes.h
+++ b/Userland/Libraries/LibJS/Runtime/ErrorTypes.h
@@ -31,6 +31,7 @@
     M(DivisionByZero, "Division by zero")                                                                                               \
     M(FinalizationRegistrySameTargetAndValue, "Target and held value must not be the same")                                             \
     M(GetCapabilitiesExecutorCalledMultipleTimes, "GetCapabilitiesExecutor was called multiple times")                                  \
+    M(GlobalEnvironmentAlreadyHasBinding, "Global environment already has binding '{}'")                                                \
     M(IndexOutOfRange, "Index {} is out of range of array length {}")                                                                   \
     M(InOperatorWithObject, "'in' operator must be used on an object")                                                                  \
     M(InstanceOfOperatorBadPrototype, "'prototype' property of {} is not an object")                                                    \
diff --git a/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.cpp b/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.cpp
index d2dbf2bb25..94d2133f57 100644
--- a/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.cpp
+++ b/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.cpp
@@ -57,7 +57,7 @@ ThrowCompletionOr<void> GlobalEnvironment::create_mutable_binding(GlobalObject&
     // 1. Let DclRec be envRec.[[DeclarativeRecord]].
     // 2. If DclRec.HasBinding(N) is true, throw a TypeError exception.
     if (MUST(m_declarative_record->has_binding(name)))
-        return vm().throw_completion<TypeError>(global_object, ErrorType::FixmeAddAnErrorString);
+        return vm().throw_completion<TypeError>(global_object, ErrorType::GlobalEnvironmentAlreadyHasBinding, name);
 
     // 3. Return DclRec.CreateMutableBinding(N, D).
     return m_declarative_record->create_mutable_binding(global_object, name, can_be_deleted);
@@ -69,7 +69,7 @@ ThrowCompletionOr<void> GlobalEnvironment::create_immutable_binding(GlobalObject
     // 1. Let DclRec be envRec.[[DeclarativeRecord]].
     // 2. If DclRec.HasBinding(N) is true, throw a TypeError exception.
     if (MUST(m_declarative_record->has_binding(name)))
-        return vm().throw_completion<TypeError>(global_object, ErrorType::FixmeAddAnErrorString);
+        return vm().throw_completion<TypeError>(global_object, ErrorType::GlobalEnvironmentAlreadyHasBinding, name);
 
     // 3. Return DclRec.CreateImmutableBinding(N, S).
     return m_declarative_record->create_immutable_binding(global_object, name, strict);