diff --git a/config/common/errors.go b/config/common/errors.go
index a5f8d5b2..9622a5b6 100644
--- a/config/common/errors.go
+++ b/config/common/errors.go
@@ -29,6 +29,7 @@ var (
 	// high-level errors for fatal reports
 	ErrInvalidSourceConfig    = errors.New("source config is invalid")
 	ErrInvalidGeneratedConfig = errors.New("config generated was invalid")
+	ErrInvalidFileExtension   = errors.New("file type provided was invalid; use .ign for local/inline instead")
 
 	// deprecated variant/version
 	ErrRhcosVariantUnsupported = errors.New("rhcos variant has been removed; use openshift variant instead: https://coreos.github.io/butane/upgrading-openshift/")
diff --git a/config/fcos/v1_6_exp/validate.go b/config/fcos/v1_6_exp/validate.go
index 4c3ae9de..58df0230 100644
--- a/config/fcos/v1_6_exp/validate.go
+++ b/config/fcos/v1_6_exp/validate.go
@@ -27,6 +27,7 @@ import (
 const rootDevice = "/dev/disk/by-id/coreos-boot-disk"
 
 var allowedMountpoints = regexp.MustCompile(`^/(etc|var)(/|$)`)
+var fileExt = regexp.MustCompile("^(.ign)$")
 
 // We can't define a Validate function directly on Disk because that's defined in base,
 // so we use a Validate function on the top-level Config instead.
@@ -45,6 +46,18 @@ func (conf Config) Validate(c path.ContextPath) (r report.Report) {
 			r.AddOnError(c.Append("storage", "filesystems", i, "path"), common.ErrMountPointForbidden)
 		}
 	}
+
+	if conf.Ignition.Config.Merge != nil {
+		for i, conf := range conf.Ignition.Config.Merge {
+			if conf.Inline != nil && !fileExt.MatchString(string(*conf.Inline)) {
+				r.AddOnError(c.Append("ignition", "config", "merge", i, "inline"), common.ErrInvalidFileExtension)
+			}
+
+			if conf.Local != nil && !fileExt.MatchString(string(*conf.Local)) {
+				r.AddOnError(c.Append("ignition", "config", "merge", i, "local"), common.ErrInvalidFileExtension)
+			}
+		}
+	}
 	return
 }
 
diff --git a/config/fcos/v1_6_exp/validate_test.go b/config/fcos/v1_6_exp/validate_test.go
index 2c850580..e313e396 100644
--- a/config/fcos/v1_6_exp/validate_test.go
+++ b/config/fcos/v1_6_exp/validate_test.go
@@ -479,3 +479,38 @@ func TestValidateConfig(t *testing.T) {
 		})
 	}
 }
+
+func TestValidateFileExtension(t *testing.T) {
+	tests := []struct {
+		in      Config
+		out     error
+		errPath path.ContextPath
+	}{
+		{
+			in: Config{
+				Config: base.Config{
+					Ignition: base.Ignition{
+						Config: base.IgnitionConfig{
+							Merge: []base.Resource{
+								{
+									Inline: util.StrToPtr("config.bu"),
+								},
+							},
+						},
+					},
+				},
+			},
+			out:     common.ErrInvalidFileExtension,
+			errPath: path.New("yaml", "ignition", "config", "merge", 0, "inline"),
+		},
+	}
+	for i, test := range tests {
+		t.Run(fmt.Sprintf("validate %d", i), func(t *testing.T) {
+			actual := test.in.Validate(path.New("yaml"))
+			baseutil.VerifyReport(t, test.in, actual)
+			expected := report.Report{}
+			expected.AddOnError(test.errPath, test.out)
+			assert.Equal(t, expected, actual, "invalid report")
+		})
+	}
+}
diff --git a/docs/release-notes.md b/docs/release-notes.md
index f7596971..16755739 100644
--- a/docs/release-notes.md
+++ b/docs/release-notes.md
@@ -21,6 +21,8 @@ key](https://getfedora.org/security/).
   openshift 4.14.0-exp)_
 - Require `storage.filesystems.path` to start with `/etc` or `/var` if
   `with_mount_unit` is true _(fcos 1.6.0-exp, openshift 4.14.0-exp)_
+- Require local/inline fields from Ignition.Config.Merge to have the .ign file 
+  extension _(fcos 1.6.0-exp)_
 
 ### Bug fixes