diff --git a/builtin/providers/test/resource_config_mode_test.go b/builtin/providers/test/resource_config_mode_test.go
index a63de5c61..743e8e9e9 100644
--- a/builtin/providers/test/resource_config_mode_test.go
+++ b/builtin/providers/test/resource_config_mode_test.go
@@ -43,6 +43,41 @@ resource "test_resource_config_mode" "foo" {
 			},
 			resource.TestStep{
 				Config: strings.TrimSpace(`
+resource "test_resource_config_mode" "foo" {
+	# Due to a preprocessing fixup we do in lang.EvalBlock, it's allowed
+	# to specify resource_as_attr members using one or more nested blocks
+	# instead of attribute syntax, if desired. This should be equivalent
+	# to the previous config.
+	#
+	# This allowance is made for backward-compatibility with existing providers
+	# before Terraform v0.12 that were expecting nested block types to also
+	# support attribute syntax; it should not be used for any new use-cases.
+	resource_as_attr {
+		foo = "resource_as_attr 0"
+	}
+	resource_as_attr {
+		foo = "resource_as_attr 1"
+	}
+	resource_as_attr_dynamic = [
+		{
+			foo = "resource_as_attr_dynamic 0"
+		},
+		{
+		},
+	]
+}
+				`),
+				Check: resource.ComposeTestCheckFunc(
+					resource.TestCheckResourceAttr("test_resource_config_mode.foo", "resource_as_attr.#", "2"),
+					resource.TestCheckResourceAttr("test_resource_config_mode.foo", "resource_as_attr.0.foo", "resource_as_attr 0"),
+					resource.TestCheckResourceAttr("test_resource_config_mode.foo", "resource_as_attr.1.foo", "resource_as_attr 1"),
+					resource.TestCheckResourceAttr("test_resource_config_mode.foo", "resource_as_attr_dynamic.#", "2"),
+					resource.TestCheckResourceAttr("test_resource_config_mode.foo", "resource_as_attr_dynamic.0.foo", "resource_as_attr_dynamic 0"),
+					resource.TestCheckResourceAttr("test_resource_config_mode.foo", "resource_as_attr_dynamic.1.foo", "default"),
+				),
+			},
+			resource.TestStep{
+				Config: strings.TrimSpace(`
 resource "test_resource_config_mode" "foo" {
 	resource_as_attr = [
 		{
diff --git a/lang/eval.go b/lang/eval.go
index e27ff30e1..5ad1eef2a 100644
--- a/lang/eval.go
+++ b/lang/eval.go
@@ -5,12 +5,12 @@ import (
 	"log"
 	"strconv"
 
-	"github.com/hashicorp/terraform/addrs"
-
 	"github.com/hashicorp/hcl2/ext/dynblock"
 	"github.com/hashicorp/hcl2/hcl"
 	"github.com/hashicorp/hcl2/hcldec"
+	"github.com/hashicorp/terraform/addrs"
 	"github.com/hashicorp/terraform/configs/configschema"
+	"github.com/hashicorp/terraform/lang/blocktoattr"
 	"github.com/hashicorp/terraform/tfdiags"
 	"github.com/zclconf/go-cty/cty"
 	"github.com/zclconf/go-cty/cty/convert"
@@ -58,6 +58,14 @@ func (s *Scope) EvalBlock(body hcl.Body, schema *configschema.Block) (cty.Value,
 		return cty.UnknownVal(schema.ImpliedType()), diags
 	}
 
+	// HACK: In order to remain compatible with some assumptions made in
+	// Terraform v0.11 and earlier about the approximate equivalence of
+	// attribute vs. block syntax, we do a just-in-time fixup here to allow
+	// any attribute in the schema that has a list-of-objects or set-of-objects
+	// kind to potentially be populated instead by one or more nested blocks
+	// whose type is the attribute name.
+	body = blocktoattr.FixUpBlockAttrs(body, schema)
+
 	val, evalDiags := hcldec.Decode(body, spec, ctx)
 	diags = diags.Append(evalDiags)