diff --git a/builtin/providers/test/resource_nested_set_test.go b/builtin/providers/test/resource_nested_set_test.go
index fac38ef6d..fd05f6c12 100644
--- a/builtin/providers/test/resource_nested_set_test.go
+++ b/builtin/providers/test/resource_nested_set_test.go
@@ -620,3 +620,39 @@ resource "test_resource_nested_set" "bar" {
 		},
 	})
 }
+
+func TestResourceNestedSet_dynamicSetBlock(t *testing.T) {
+	resource.UnitTest(t, resource.TestCase{
+		Providers:    testAccProviders,
+		CheckDestroy: testAccCheckResourceDestroy,
+		Steps: []resource.TestStep{
+			resource.TestStep{
+				Config: strings.TrimSpace(`
+resource "test_resource" "a" {
+	required = "ok"
+	required_map = {
+		a = "b"
+	}
+}
+
+resource "test_resource_nested_set" "foo" {
+  dynamic "with_list" {
+    iterator = thing
+	for_each = test_resource.a.computed_list
+    content {
+      required = thing.value
+	  list = [thing.key]
+    }
+  }
+}
+				`),
+				Check: resource.ComposeTestCheckFunc(
+					func(s *terraform.State) error {
+						fmt.Println(s)
+						return nil
+					},
+				),
+			},
+		},
+	})
+}
diff --git a/plans/objchange/compatible.go b/plans/objchange/compatible.go
index 8a74c07fe..d85086c97 100644
--- a/plans/objchange/compatible.go
+++ b/plans/objchange/compatible.go
@@ -169,6 +169,16 @@ func assertObjectCompatible(schema *configschema.Block, planned, actual cty.Valu
 			})
 			errs = append(errs, setErrs...)
 
+			if maybeUnknownBlocks {
+				// When unknown blocks are present the final number of blocks
+				// may be different, either because the unknown set values
+				// become equal and are collapsed, or the count is unknown due
+				// a dynamic block. Unfortunately this means we can't do our
+				// usual checks in this case without generating false
+				// negatives.
+				continue
+			}
+
 			// There can be fewer elements in a set after its elements are all
 			// known (values that turn out to be equal will coalesce) but the
 			// number of elements must never get larger.
diff --git a/plans/objchange/compatible_test.go b/plans/objchange/compatible_test.go
index 2841ec26b..473ee5119 100644
--- a/plans/objchange/compatible_test.go
+++ b/plans/objchange/compatible_test.go
@@ -1068,9 +1068,9 @@ func TestAssertObjectCompatible(t *testing.T) {
 					}),
 				}),
 			}),
-			[]string{
-				`.block: block set length changed from 2 to 3`,
-			},
+			// there is no error here, because the presence of unknowns
+			// indicates this may be a dynamic block, and the length is unknown
+			nil,
 		},
 		{
 			&configschema.Block{
@@ -1135,6 +1135,34 @@ func TestAssertObjectCompatible(t *testing.T) {
 			}),
 			nil,
 		},
+		{
+			&configschema.Block{
+				BlockTypes: map[string]*configschema.NestedBlock{
+					"block": {
+						Nesting: configschema.NestingSet,
+						Block:   schemaWithFoo,
+					},
+				},
+			},
+			cty.ObjectVal(map[string]cty.Value{
+				"block": cty.SetVal([]cty.Value{
+					cty.ObjectVal(map[string]cty.Value{
+						"foo": cty.UnknownVal(cty.String),
+					}),
+				}),
+			}),
+			cty.ObjectVal(map[string]cty.Value{
+				"block": cty.SetVal([]cty.Value{
+					cty.ObjectVal(map[string]cty.Value{
+						"foo": cty.StringVal("a"),
+					}),
+					cty.ObjectVal(map[string]cty.Value{
+						"foo": cty.StringVal("b"),
+					}),
+				}),
+			}),
+			nil,
+		},
 		{
 			&configschema.Block{
 				BlockTypes: map[string]*configschema.NestedBlock{