diff --git a/builtin/providers/test/resource_map.go b/builtin/providers/test/resource_map.go
index 38f684106..12b9e2535 100644
--- a/builtin/providers/test/resource_map.go
+++ b/builtin/providers/test/resource_map.go
@@ -3,6 +3,7 @@ package test
 import (
 	"fmt"
 
+	"github.com/hashicorp/terraform/config"
 	"github.com/hashicorp/terraform/helper/schema"
 )
 
@@ -22,6 +23,15 @@ func testResourceMap() *schema.Resource {
 				Type:     schema.TypeMap,
 				Optional: true,
 				Elem:     &schema.Schema{Type: schema.TypeString},
+				ValidateFunc: func(v interface{}, _ string) ([]string, []error) {
+					errs := []error{}
+					for k, v := range v.(map[string]interface{}) {
+						if v == config.UnknownVariableValue {
+							errs = append(errs, fmt.Errorf("unknown value in ValidateFunc: %q=%q", k, v))
+						}
+					}
+					return nil, errs
+				},
 			},
 			"map_values": {
 				Type:     schema.TypeMap,
diff --git a/builtin/providers/test/resource_map_test.go b/builtin/providers/test/resource_map_test.go
index 6e279b7f5..0d82d5f4f 100644
--- a/builtin/providers/test/resource_map_test.go
+++ b/builtin/providers/test/resource_map_test.go
@@ -31,6 +31,35 @@ resource "test_resource_map" "foobar" {
 	})
 }
 
+func TestResourceMap_basicWithVars(t *testing.T) {
+	resource.UnitTest(t, resource.TestCase{
+		Providers:    testAccProviders,
+		CheckDestroy: testAccCheckResourceDestroy,
+		Steps: []resource.TestStep{
+			{
+				Config: `
+variable "a" {
+  default = "a"
+}
+
+variable "b" {
+  default = "b"
+}
+
+resource "test_resource_map" "foobar" {
+	name = "test"
+	map_of_three = {
+		one   = var.a
+		two   = var.b
+		empty = ""
+	}
+}`,
+				Check: resource.ComposeTestCheckFunc(),
+			},
+		},
+	})
+}
+
 func TestResourceMap_computedMap(t *testing.T) {
 	resource.UnitTest(t, resource.TestCase{
 		Providers:    testAccProviders,
diff --git a/helper/schema/schema.go b/helper/schema/schema.go
index 6a3c15a64..26b180e03 100644
--- a/helper/schema/schema.go
+++ b/helper/schema/schema.go
@@ -1365,10 +1365,12 @@ func (m schemaMap) validate(
 			"%q: this field cannot be set", k)}
 	}
 
-	if raw == config.UnknownVariableValue {
-		// If the value is unknown then we can't validate it yet.
-		// In particular, this avoids spurious type errors where downstream
-		// validation code sees UnknownVariableValue as being just a string.
+	// If the value is unknown then we can't validate it yet.
+	// In particular, this avoids spurious type errors where downstream
+	// validation code sees UnknownVariableValue as being just a string.
+	// The SDK has to allow the unknown value through initially, so that
+	// Required fields set via an interpolated value are accepted.
+	if !isWhollyKnown(raw) {
 		return nil, nil
 	}
 
@@ -1380,6 +1382,28 @@ func (m schemaMap) validate(
 	return m.validateType(k, raw, schema, c)
 }
 
+// isWhollyKnown returns false if the argument contains an UnknownVariableValue
+func isWhollyKnown(raw interface{}) bool {
+	switch raw := raw.(type) {
+	case string:
+		if raw == config.UnknownVariableValue {
+			return false
+		}
+	case []interface{}:
+		for _, v := range raw {
+			if !isWhollyKnown(v) {
+				return false
+			}
+		}
+	case map[string]interface{}:
+		for _, v := range raw {
+			if !isWhollyKnown(v) {
+				return false
+			}
+		}
+	}
+	return true
+}
 func (m schemaMap) validateConflictingAttributes(
 	k string,
 	schema *Schema,