diff --git a/source/common/engine/namedef.h b/source/common/engine/namedef.h
index 9d5cb27ff..f79be20a5 100644
--- a/source/common/engine/namedef.h
+++ b/source/common/engine/namedef.h
@@ -152,6 +152,7 @@ xx(stateinfo)
 xx(DamageFunction)
 xx(Length)
 xx(LengthSquared)
+xx(Sum)
 xx(Unit)
 xx(Angle)
 xx(PlusZ)
diff --git a/source/common/scripting/backend/codegen.cpp b/source/common/scripting/backend/codegen.cpp
index 6f6a8e025..5c6d2171e 100644
--- a/source/common/scripting/backend/codegen.cpp
+++ b/source/common/scripting/backend/codegen.cpp
@@ -8273,7 +8273,7 @@ FxExpression *FxMemberFunctionCall::Resolve(FCompileContext& ctx)
 	else if (Self->IsVector())
 	{
 		// handle builtins: Vectors got 5.
-		if (MethodName == NAME_Length || MethodName == NAME_LengthSquared || MethodName == NAME_Unit || MethodName == NAME_Angle)
+		if (MethodName == NAME_Length || MethodName == NAME_LengthSquared || MethodName == NAME_Sum || MethodName == NAME_Unit || MethodName == NAME_Angle)
 		{
 			if (ArgList.Size() > 0)
 			{
@@ -9280,6 +9280,7 @@ FxExpression *FxVectorBuiltin::Resolve(FCompileContext &ctx)
 	{
 	case NAME_Length:
 	case NAME_LengthSquared:
+	case NAME_Sum:
 	case NAME_Angle:
 		ValueType = TypeFloat64;
 		break;
@@ -9312,6 +9313,23 @@ ExpEmit FxVectorBuiltin::Emit(VMFunctionBuilder *build)
 	{
 		build->Emit(vecSize == 2 ? OP_DOTV2_RR : vecSize == 3 ? OP_DOTV3_RR : OP_DOTV4_RR, to.RegNum, op.RegNum, op.RegNum);
 	}
+	else if (Function == NAME_Sum)
+	{
+		ExpEmit temp(build, ValueType->GetRegType(), 1);
+		build->Emit(OP_FLOP, to.RegNum, op.RegNum, FLOP_ABS);
+		build->Emit(OP_FLOP, temp.RegNum, op.RegNum + 1, FLOP_ABS);
+		build->Emit(OP_ADDF_RR, to.RegNum, to.RegNum, temp.RegNum);
+		if (vecSize > 2)
+		{
+			build->Emit(OP_FLOP, temp.RegNum, op.RegNum + 2, FLOP_ABS);
+			build->Emit(OP_ADDF_RR, to.RegNum, to.RegNum, temp.RegNum);
+		}
+		if (vecSize > 3)
+		{
+			build->Emit(OP_FLOP, temp.RegNum, op.RegNum + 3, FLOP_ABS);
+			build->Emit(OP_ADDF_RR, to.RegNum, to.RegNum, temp.RegNum);
+		}
+	}
 	else if (Function == NAME_Unit)
 	{
 		ExpEmit len(build, REGT_FLOAT);