diff --git a/flatmap/expand.go b/flatmap/expand.go
index e0b81b641..1449065e9 100644
--- a/flatmap/expand.go
+++ b/flatmap/expand.go
@@ -60,6 +60,11 @@ func expandArray(m map[string]string, prefix string) []interface{} {
 		return []interface{}{}
 	}
 
+	// NOTE: "num" is not necessarily accurate, e.g. if a user tampers
+	// with state, so the following code should not crash when given a
+	// number of items more or less than what's given in num. The
+	// num key is mainly just a hint that this is a list or set.
+
 	// 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.
@@ -101,7 +106,7 @@ func expandArray(m map[string]string, prefix string) []interface{} {
 	}
 	sort.Ints(keysList)
 
-	result := make([]interface{}, num)
+	result := make([]interface{}, len(keysList))
 	for i, key := range keysList {
 		keyString := strconv.Itoa(key)
 		if computed[keyString] {
diff --git a/flatmap/expand_test.go b/flatmap/expand_test.go
index c0fa83211..a64eb9c54 100644
--- a/flatmap/expand_test.go
+++ b/flatmap/expand_test.go
@@ -35,6 +35,40 @@ func TestExpand(t *testing.T) {
 			},
 		},
 
+		{
+			Map: map[string]string{
+				// # mismatches actual number of keys; actual number should
+				// "win" here, since the # is just a hint that this is a list.
+				"foo.#": "1",
+				"foo.0": "one",
+				"foo.1": "two",
+				"foo.2": "three",
+			},
+			Key: "foo",
+			Output: []interface{}{
+				"one",
+				"two",
+				"three",
+			},
+		},
+
+		{
+			Map: map[string]string{
+				// # mismatches actual number of keys; actual number should
+				// "win" here, since the # is just a hint that this is a list.
+				"foo.#": "5",
+				"foo.0": "one",
+				"foo.1": "two",
+				"foo.2": "three",
+			},
+			Key: "foo",
+			Output: []interface{}{
+				"one",
+				"two",
+				"three",
+			},
+		},
+
 		{
 			Map: map[string]string{
 				"foo.#":         "1",