diff --git a/flatmap/expand.go b/flatmap/expand.go
index b2072a62f..331357ff3 100644
--- a/flatmap/expand.go
+++ b/flatmap/expand.go
@@ -2,6 +2,7 @@ package flatmap
 
 import (
 	"fmt"
+	"sort"
 	"strconv"
 	"strings"
 )
@@ -42,9 +43,43 @@ func expandArray(m map[string]string, prefix string) []interface{} {
 		panic(err)
 	}
 
+	// The Schema "Set" type stores its values in an array format, but using
+	// numeric hash values instead of ordinal keys. Take the set of keys
+	// regardless of value, and expand them in numeric order.
+	// See GH-11042 for more details.
+	keySet := map[int]bool{}
+	for k := range m {
+		if !strings.HasPrefix(k, prefix+".") {
+			continue
+		}
+
+		key := k[len(prefix)+1:]
+		idx := strings.Index(key, ".")
+		if idx != -1 {
+			key = key[:idx]
+		}
+
+		// skip the count value
+		if key == "#" {
+			continue
+		}
+
+		k, err := strconv.Atoi(key)
+		if err != nil {
+			panic(err)
+		}
+		keySet[int(k)] = true
+	}
+
+	keysList := make([]int, 0, num)
+	for key := range keySet {
+		keysList = append(keysList, key)
+	}
+	sort.Ints(keysList)
+
 	result := make([]interface{}, num)
-	for i := 0; i < int(num); i++ {
-		result[i] = Expand(m, fmt.Sprintf("%s.%d", prefix, i))
+	for i, key := range keysList {
+		result[i] = Expand(m, fmt.Sprintf("%s.%d", prefix, key))
 	}
 
 	return result
diff --git a/flatmap/expand_test.go b/flatmap/expand_test.go
index b480e2ca9..b5da3197b 100644
--- a/flatmap/expand_test.go
+++ b/flatmap/expand_test.go
@@ -106,6 +106,17 @@ func TestExpand(t *testing.T) {
 				"list2": []interface{}{"c"},
 			},
 		},
+
+		{
+			Map: map[string]string{
+				"set.#":    "3",
+				"set.1234": "a",
+				"set.1235": "b",
+				"set.1236": "c",
+			},
+			Key:    "set",
+			Output: []interface{}{"a", "b", "c"},
+		},
 	}
 
 	for _, tc := range cases {
diff --git a/terraform/interpolate_test.go b/terraform/interpolate_test.go
index 9c6cdc40e..54f762fe7 100644
--- a/terraform/interpolate_test.go
+++ b/terraform/interpolate_test.go
@@ -838,6 +838,44 @@ func TestInterpolator_nestedMapsAndLists(t *testing.T) {
 		interfaceToVariableSwallowError(mapOfList))
 }
 
+func TestInterpolator_sets(t *testing.T) {
+	state := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: rootModulePath,
+				Resources: map[string]*ResourceState{
+					"aws_network_interface.set": &ResourceState{
+						Type:         "aws_network_interface",
+						Dependencies: []string{},
+						Primary: &InstanceState{
+							ID: "null",
+							Attributes: map[string]string{
+								"private_ips.#":          "1",
+								"private_ips.3977356764": "10.42.16.179",
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+
+	i := &Interpolater{
+		Module:    testModule(t, "interpolate-multi-vars"),
+		StateLock: new(sync.RWMutex),
+		State:     state,
+	}
+
+	scope := &InterpolationScope{
+		Path: rootModulePath,
+	}
+
+	set := []interface{}{"10.42.16.179"}
+
+	testInterpolate(t, i, scope, "aws_network_interface.set.private_ips",
+		interfaceToVariableSwallowError(set))
+}
+
 func testInterpolate(
 	t *testing.T, i *Interpolater,
 	scope *InterpolationScope,