diff --git a/go/src/miller/dsl/cst/udf.go b/go/src/miller/dsl/cst/udf.go
index 93555b98e..11f00d3d2 100644
--- a/go/src/miller/dsl/cst/udf.go
+++ b/go/src/miller/dsl/cst/udf.go
@@ -19,6 +19,7 @@ type Signature struct {
 	functionName            string
 	arity                   int // Computable from len(typeGatedParameterNames) at callee, not at caller
 	typeGatedParameterNames []*types.TypeGatedMlrvalName
+	typeGatedReturnValue    *types.TypeGatedMlrvalName
 
 	// TODO: parameter typedecls
 	// TODO: return-value typedecls
@@ -28,11 +29,13 @@ func NewSignature(
 	functionName string,
 	arity int,
 	typeGatedParameterNames []*types.TypeGatedMlrvalName,
+	typeGatedReturnValue *types.TypeGatedMlrvalName,
 ) *Signature {
 	return &Signature{
 		functionName:            functionName,
 		arity:                   arity,
 		typeGatedParameterNames: typeGatedParameterNames,
+		typeGatedReturnValue:    typeGatedReturnValue,
 	}
 }
 
@@ -58,7 +61,7 @@ func NewUnresolvedUDF(
 	functionName string,
 	callsiteArity int,
 ) *UDF {
-	signature := NewSignature(functionName, callsiteArity, nil)
+	signature := NewSignature(functionName, callsiteArity, nil, nil)
 	udf := NewUDF(signature, nil)
 	return udf
 }
@@ -132,6 +135,16 @@ func (this *UDFCallsite) Evaluate(state *State) types.Mlrval {
 	// their UDF but we lost the return value.
 	lib.InternalCodingErrorIf(blockExitPayload.blockReturnValue == nil)
 
+	err = this.udf.signature.typeGatedReturnValue.Check(blockExitPayload.blockReturnValue)
+	if err != nil {
+		// TODO: put error-return in the Evaluate API
+		fmt.Fprint(
+			os.Stderr,
+			err,
+		)
+		os.Exit(1)
+	}
+
 	return *blockExitPayload.blockReturnValue
 }
 
@@ -216,7 +229,17 @@ func (this *RootNode) BuildAndInstallUDF(astNode *dsl.ASTNode) error {
 	functionName := string(astNode.Token.Lit)
 	parameterListASTNode := astNode.Children[0]
 	functionBodyASTNode := astNode.Children[1]
-	// TODO: optional typedecl 3rd arg
+
+	returnValueTypeName := "var"
+	if len(astNode.Children) == 3 {
+		typeNode := astNode.Children[2]
+		lib.InternalCodingErrorIf(typeNode.Type != dsl.NodeTypeTypedecl)
+		returnValueTypeName = string(typeNode.Token.Lit)
+	}
+	typeGatedReturnValue, err := types.NewTypeGatedMlrvalName(
+		"function return value",
+		returnValueTypeName,
+	)
 
 	lib.InternalCodingErrorIf(parameterListASTNode.Type != dsl.NodeTypeParameterList)
 	lib.InternalCodingErrorIf(parameterListASTNode.Children == nil)
@@ -248,7 +271,7 @@ func (this *RootNode) BuildAndInstallUDF(astNode *dsl.ASTNode) error {
 		typeGatedParameterNames[i] = typeGatedParameterName
 	}
 
-	signature := NewSignature(functionName, arity, typeGatedParameterNames)
+	signature := NewSignature(functionName, arity, typeGatedParameterNames, typeGatedReturnValue)
 
 	functionBody, err := this.BuildStatementBlockNode(functionBodyASTNode)
 	if err != nil {
diff --git a/go/u/try-cst b/go/u/try-cst
index c5148330a..04b383277 100755
--- a/go/u/try-cst
+++ b/go/u/try-cst
@@ -429,3 +429,9 @@ run_mlr         --from u/s.dkvp put 'func f(int x) { return 2*x} $y=f(3)'
 run_mlr         --from u/s.dkvp put 'func f(num x) { return 2*x} $y=f(3)'
 mlr_expect_fail --from u/s.dkvp put 'func f(str x) { return 2*x} $y=f(3)'
 mlr_expect_fail --from u/s.dkvp put 'func f(arr x) { return 2*x} $y=f(3)'
+
+run_mlr         --from u/s.dkvp put 'func f(x): var { return 2*x} $y=f(3)'
+run_mlr         --from u/s.dkvp put 'func f(x): int { return 2*x} $y=f(3)'
+run_mlr         --from u/s.dkvp put 'func f(x): num { return 2*x} $y=f(3)'
+mlr_expect_fail --from u/s.dkvp put 'func f(x): str { return 2*x} $y=f(3)'
+mlr_expect_fail --from u/s.dkvp put 'func f(x): arr { return 2*x} $y=f(3)'
diff --git a/go/u/try-cst.out b/go/u/try-cst.out
index 2a631b9b6..91362acbe 100644
--- a/go/u/try-cst.out
+++ b/go/u/try-cst.out
@@ -3150,3 +3150,49 @@ a=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776
 a=eks,b=wye,i=4,x=0.38139939387114097,y=0.13418874328430463
 mlr --from u/s.dkvp put str x = 3
 mlr --from u/s.dkvp put arr x = 3
+
+----------------------------------------------------------------
+mlr --from u/s.dkvp put func f(var x) { return 2*x} $y=f(3)
+a=pan,b=pan,i=1,x=0.3467901443380824,y=6
+a=eks,b=pan,i=2,x=0.7586799647899636,y=6
+a=wye,b=wye,i=3,x=0.20460330576630303,y=6
+a=eks,b=wye,i=4,x=0.38139939387114097,y=6
+
+----------------------------------------------------------------
+mlr --from u/s.dkvp put func f(int x) { return 2*x} $y=f(3)
+a=pan,b=pan,i=1,x=0.3467901443380824,y=6
+a=eks,b=pan,i=2,x=0.7586799647899636,y=6
+a=wye,b=wye,i=3,x=0.20460330576630303,y=6
+a=eks,b=wye,i=4,x=0.38139939387114097,y=6
+
+----------------------------------------------------------------
+mlr --from u/s.dkvp put func f(num x) { return 2*x} $y=f(3)
+a=pan,b=pan,i=1,x=0.3467901443380824,y=6
+a=eks,b=pan,i=2,x=0.7586799647899636,y=6
+a=wye,b=wye,i=3,x=0.20460330576630303,y=6
+a=eks,b=wye,i=4,x=0.38139939387114097,y=6
+mlr --from u/s.dkvp put func f(str x) { return 2*x} $y=f(3)
+mlr --from u/s.dkvp put func f(arr x) { return 2*x} $y=f(3)
+
+----------------------------------------------------------------
+mlr --from u/s.dkvp put func f(x): var { return 2*x} $y=f(3)
+a=pan,b=pan,i=1,x=0.3467901443380824,y=6
+a=eks,b=pan,i=2,x=0.7586799647899636,y=6
+a=wye,b=wye,i=3,x=0.20460330576630303,y=6
+a=eks,b=wye,i=4,x=0.38139939387114097,y=6
+
+----------------------------------------------------------------
+mlr --from u/s.dkvp put func f(x): int { return 2*x} $y=f(3)
+a=pan,b=pan,i=1,x=0.3467901443380824,y=6
+a=eks,b=pan,i=2,x=0.7586799647899636,y=6
+a=wye,b=wye,i=3,x=0.20460330576630303,y=6
+a=eks,b=wye,i=4,x=0.38139939387114097,y=6
+
+----------------------------------------------------------------
+mlr --from u/s.dkvp put func f(x): num { return 2*x} $y=f(3)
+a=pan,b=pan,i=1,x=0.3467901443380824,y=6
+a=eks,b=pan,i=2,x=0.7586799647899636,y=6
+a=wye,b=wye,i=3,x=0.20460330576630303,y=6
+a=eks,b=wye,i=4,x=0.38139939387114097,y=6
+mlr --from u/s.dkvp put func f(x): str { return 2*x} $y=f(3)
+mlr --from u/s.dkvp put func f(x): arr { return 2*x} $y=f(3)