diff --git a/hcl2template/function/datetime.go b/hcl2template/function/datetime.go
index 066db18db39..a2b0cc9d17c 100644
--- a/hcl2template/function/datetime.go
+++ b/hcl2template/function/datetime.go
@@ -12,19 +12,20 @@ import (
 	"github.com/zclconf/go-cty/cty/function"
 )
 
-// InitTime is the UTC time when this package was initialized. It is
+// initTime is the UTC time when this package was initialized. It is
 // used as the timestamp for all configuration templates so that they
 // match for a single build.
-var InitTime time.Time
+var initTime time.Time
 
 func init() {
-	InitTime = time.Now().UTC()
+	initTime = time.Now().UTC()
 }
 
 // TimestampFunc constructs a function that returns a string representation of the current date and time.
 var TimestampFunc = function.New(&function.Spec{
-	Params: []function.Parameter{},
-	Type:   function.StaticReturnType(cty.String),
+	Params:       []function.Parameter{},
+	Type:         function.StaticReturnType(cty.String),
+	RefineResult: refineNotNull,
 	Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
 		return cty.StringVal(time.Now().UTC().Format(time.RFC3339)), nil
 	},
@@ -40,42 +41,46 @@ func Timestamp() (cty.Value, error) {
 }
 
 // LegacyIsotimeFunc constructs a function that returns a string representation
-// of the current date and time using golang's datetime formatting.
+// of the current date and time using the Go language datetime formatting syntax.
 var LegacyIsotimeFunc = function.New(&function.Spec{
 	Params: []function.Parameter{},
 	VarParam: &function.Parameter{
 		Name: "format",
 		Type: cty.String,
 	},
-	Type: function.StaticReturnType(cty.String),
+	Type:         function.StaticReturnType(cty.String),
+	RefineResult: refineNotNull,
 	Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
 		if len(args) > 1 {
 			return cty.StringVal(""), fmt.Errorf("too many values, 1 needed: %v", args)
-		} else if len(args) == 0 {
-			return cty.StringVal(InitTime.Format(time.RFC3339)), nil
+		}
+		if len(args) == 0 {
+			return cty.StringVal(initTime.Format(time.RFC3339)), nil
 		}
 		format := args[0].AsString()
-		return cty.StringVal(InitTime.Format(format)), nil
+		return cty.StringVal(initTime.Format(format)), nil
 	},
 })
 
 // LegacyStrftimeFunc constructs a function that returns a string representation
-// of the current date and time using golang's strftime datetime formatting.
+// of the current date and time using the Go language strftime datetime formatting syntax.
 var LegacyStrftimeFunc = function.New(&function.Spec{
 	Params: []function.Parameter{},
 	VarParam: &function.Parameter{
 		Name: "format",
 		Type: cty.String,
 	},
-	Type: function.StaticReturnType(cty.String),
+	Type:         function.StaticReturnType(cty.String),
+	RefineResult: refineNotNull,
 	Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
 		if len(args) > 1 {
 			return cty.StringVal(""), fmt.Errorf("too many values, 1 needed: %v", args)
-		} else if len(args) == 0 {
-			return cty.StringVal(InitTime.Format(time.RFC3339)), nil
+		}
+		if len(args) == 0 {
+			return cty.StringVal(initTime.Format(time.RFC3339)), nil
 		}
 		format := args[0].AsString()
-		return cty.StringVal(strftime.Format(format, InitTime)), nil
+		return cty.StringVal(strftime.Format(format, initTime)), nil
 	},
 })
 
diff --git a/hcl2template/function/env.go b/hcl2template/function/env.go
index 34c09a8b921..b6c36e68494 100644
--- a/hcl2template/function/env.go
+++ b/hcl2template/function/env.go
@@ -21,7 +21,8 @@ var EnvFunc = function.New(&function.Spec{
 			AllowUnknown: false,
 		},
 	},
-	Type: function.StaticReturnType(cty.String),
+	Type:         function.StaticReturnType(cty.String),
+	RefineResult: refineNotNull,
 	Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
 		key := args[0].AsString()
 		value := os.Getenv(key)
diff --git a/hcl2template/function/index.go b/hcl2template/function/index.go
index cb4f0c51921..8aade576ded 100644
--- a/hcl2template/function/index.go
+++ b/hcl2template/function/index.go
@@ -23,7 +23,8 @@ var IndexFunc = function.New(&function.Spec{
 			Type: cty.DynamicPseudoType,
 		},
 	},
-	Type: function.StaticReturnType(cty.Number),
+	Type:         function.StaticReturnType(cty.Number),
+	RefineResult: refineNotNull,
 	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
 		if !(args[0].Type().IsListType() || args[0].Type().IsTupleType()) {
 			return cty.NilVal, errors.New("argument must be a list or tuple")
diff --git a/hcl2template/function/length.go b/hcl2template/function/length.go
index 23b5969af10..f2b83dad925 100644
--- a/hcl2template/function/length.go
+++ b/hcl2template/function/length.go
@@ -29,6 +29,7 @@ var LengthFunc = function.New(&function.Spec{
 			return cty.Number, errors.New("argument must be a string, a collection type, or a structural type")
 		}
 	},
+	RefineResult: refineNotNull,
 	Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
 		coll := args[0]
 		collTy := args[0].Type()
diff --git a/hcl2template/function/length_test.go b/hcl2template/function/length_test.go
index 0a68c126c51..9bae3886f74 100644
--- a/hcl2template/function/length_test.go
+++ b/hcl2template/function/length_test.go
@@ -5,6 +5,7 @@ package function
 
 import (
 	"fmt"
+	"math"
 	"testing"
 
 	"github.com/zclconf/go-cty/cty"
@@ -69,11 +70,15 @@ func TestLength(t *testing.T) {
 		},
 		{
 			cty.UnknownVal(cty.List(cty.Bool)),
-			cty.UnknownVal(cty.Number),
+			cty.UnknownVal(cty.Number).Refine().
+				NotNull().
+				NumberRangeLowerBound(cty.Zero, true).
+				NumberRangeUpperBound(cty.NumberIntVal(math.MaxInt), true).
+				NewValue(),
 		},
 		{
 			cty.DynamicVal,
-			cty.UnknownVal(cty.Number),
+			cty.UnknownVal(cty.Number).RefineNotNull(),
 		},
 		{
 			cty.StringVal("hello"),
@@ -118,11 +123,10 @@ func TestLength(t *testing.T) {
 		},
 		{
 			cty.UnknownVal(cty.String),
-			cty.UnknownVal(cty.Number),
-		},
-		{
-			cty.DynamicVal,
-			cty.UnknownVal(cty.Number),
+			cty.UnknownVal(cty.Number).Refine().
+				NotNull().
+				NumberRangeLowerBound(cty.Zero, true).
+				NewValue(),
 		},
 	}
 
diff --git a/hcl2template/function/refinements.go b/hcl2template/function/refinements.go
new file mode 100644
index 00000000000..99314d7ee48
--- /dev/null
+++ b/hcl2template/function/refinements.go
@@ -0,0 +1,9 @@
+package function
+
+import (
+	"github.com/zclconf/go-cty/cty"
+)
+
+func refineNotNull(b *cty.RefinementBuilder) *cty.RefinementBuilder {
+	return b.NotNull()
+}