diff --git a/Compiler/NFFrontEnd/NFBuiltinCall.mo b/Compiler/NFFrontEnd/NFBuiltinCall.mo
index a868169d2a9..9430f4dc577 100644
--- a/Compiler/NFFrontEnd/NFBuiltinCall.mo
+++ b/Compiler/NFFrontEnd/NFBuiltinCall.mo
@@ -59,6 +59,7 @@ protected
   import Typing = NFTyping;
   import Util;
   import ExpandExp = NFExpandExp;
+  import Operator = NFOperator;
 
 public
   function needSpecialHandling
@@ -119,12 +120,12 @@ public
       case "ones" then typeZerosOnesCall("ones", call, origin, info);
       case "potentialRoot" then typePotentialRootCall(call, origin, info);
       case "pre" then typePreCall(call, origin, info);
-      case "product" then typeSumProductCall(call, origin, info);
+      case "product" then typeProductCall(call, origin, info);
       case "root" then typeRootCall(call, origin, info);
       case "rooted" then typeRootedCall(call, origin, info);
       case "scalar" then typeScalarCall(call, origin, info);
       case "smooth" then typeSmoothCall(call, origin, info);
-      case "sum" then typeSumProductCall(call, origin, info);
+      case "sum" then typeSumCall(call, origin, info);
       case "symmetric" then typeSymmetricCall(call, origin, info);
       case "terminal" then typeDiscreteCall(call, origin, info);
       case "transpose" then typeTransposeCall(call, origin, info);
@@ -681,23 +682,109 @@ protected
     // fix return type.
   end typeMinMaxCall;
 
-  function typeSumProductCall
+  function typeSumCall
     input Call call;
     input ExpOrigin.Type origin;
     input SourceInfo info;
     output Expression callExp;
     output Type ty;
-    output Variability var;
+    output Variability variability;
   protected
-    Call argtycall;
+    ComponentRef fn_ref;
+    list<Expression> args;
+    list<NamedArg> named_args;
+    Expression arg;
+    Function fn;
+    Boolean expanded;
+    Operator op;
   algorithm
-    // TODO: Rewrite this whole thing.
-    argtycall := Call.typeMatchNormalCall(call, origin, info);
-    argtycall := Call.unboxArgs(argtycall);
-    ty := Call.typeOf(argtycall);
-    var := Call.variability(argtycall);
-    callExp := Expression.CALL(argtycall);
-  end typeSumProductCall;
+    Call.UNTYPED_CALL(ref = fn_ref, arguments = args, named_args = named_args) := call;
+    assertNoNamedParams("sum", named_args, info);
+
+    if listLength(args) <> 1 then
+      Error.addSourceMessageAndFail(Error.NO_MATCHING_FUNCTION_FOUND_NFINST,
+        {Call.toString(call), "sum(Any[:, ...]) => Any"}, info);
+    end if;
+
+    (arg, ty, variability) := Typing.typeExp(listHead(args), origin, info);
+    ty := Type.arrayElementType(ty);
+
+    if intBitAnd(origin, intBitOr(ExpOrigin.FUNCTION, ExpOrigin.ALGORITHM)) == 0 then
+      (arg, expanded) := ExpandExp.expand(arg);
+    else
+      expanded := false;
+    end if;
+
+    if expanded then
+      args := Expression.arrayScalarElements(arg);
+
+      if listEmpty(args) then
+        callExp := Expression.makeZero(ty);
+      else
+        callExp :: args := args;
+        op := Operator.makeAdd(ty);
+
+        for e in args loop
+          callExp := Expression.BINARY(callExp, op, e);
+        end for;
+      end if;
+    else
+      {fn} := Function.typeRefCache(fn_ref);
+      callExp := Expression.CALL(Call.makeTypedCall(fn, {arg}, variability, ty));
+    end if;
+  end typeSumCall;
+
+  function typeProductCall
+    input Call call;
+    input ExpOrigin.Type origin;
+    input SourceInfo info;
+    output Expression callExp;
+    output Type ty;
+    output Variability variability;
+  protected
+    ComponentRef fn_ref;
+    list<Expression> args;
+    list<NamedArg> named_args;
+    Expression arg;
+    Function fn;
+    Boolean expanded;
+    Operator op;
+  algorithm
+    Call.UNTYPED_CALL(ref = fn_ref, arguments = args, named_args = named_args) := call;
+    assertNoNamedParams("product", named_args, info);
+
+    if listLength(args) <> 1 then
+      Error.addSourceMessageAndFail(Error.NO_MATCHING_FUNCTION_FOUND_NFINST,
+        {Call.toString(call), "product(Any[:, ...]) => Any"}, info);
+    end if;
+
+    (arg, ty, variability) := Typing.typeExp(listHead(args), origin, info);
+    ty := Type.arrayElementType(ty);
+
+    if intBitAnd(origin, intBitOr(ExpOrigin.FUNCTION, ExpOrigin.ALGORITHM)) == 0 then
+      (arg, expanded) := ExpandExp.expand(arg);
+    else
+      expanded := false;
+    end if;
+
+    if expanded then
+      args := Expression.arrayScalarElements(arg);
+
+      if listEmpty(args) then
+        callExp := Expression.makeOne(ty);
+      else
+        callExp :: args := args;
+        op := Operator.makeMul(ty);
+
+        for e in args loop
+          callExp := Expression.BINARY(callExp, op, e);
+        end for;
+      end if;
+    else
+      {fn} := Function.typeRefCache(fn_ref);
+      callExp := Expression.CALL(Call.makeTypedCall(fn, {arg}, variability, ty));
+    end if;
+  end typeProductCall;
 
   function typeSmoothCall
     input Call call;
@@ -884,7 +971,6 @@ protected
     list<Expression> args;
     list<NamedArg> named_args;
     Expression arg;
-    Variability var;
     Function fn;
     Boolean expanded;
   algorithm