diff --git a/.changelog/33704.txt b/.changelog/33704.txt
new file mode 100644
index 00000000000..37d05782fbc
--- /dev/null
+++ b/.changelog/33704.txt
@@ -0,0 +1,6 @@
+```release-note:bug
+resource/aws_db_parameter_group: Group names containing periods (`.`) no longer fail validation
+```
+```release-note:bug
+resource/aws_rds_cluster_parameter_group: Group names containing periods (`.`) no longer fail validation
+```
diff --git a/internal/service/rds/validate.go b/internal/service/rds/validate.go
index 6a627922034..1647dc456f3 100644
--- a/internal/service/rds/validate.go
+++ b/internal/service/rds/validate.go
@@ -70,9 +70,9 @@ func validOptionGroupNamePrefix(v interface{}, k string) (ws []string, errors []
 
 func validParamGroupName(v interface{}, k string) (ws []string, errors []error) {
 	value := v.(string)
-	if !regexache.MustCompile(`^[0-9a-z-]+$`).MatchString(value) {
+	if !regexache.MustCompile(`^[0-9a-z.-]+$`).MatchString(value) {
 		errors = append(errors, fmt.Errorf(
-			"only lowercase alphanumeric characters and hyphens allowed in parameter group %q", k))
+			"only lowercase alphanumeric characters, periods, and hyphens allowed in parameter group %q", k))
 	}
 	if !regexache.MustCompile(`^[a-z]`).MatchString(value) {
 		errors = append(errors, fmt.Errorf(
diff --git a/internal/service/rds/validate_test.go b/internal/service/rds/validate_test.go
index 49c9554c39c..c02eee2c064 100644
--- a/internal/service/rds/validate_test.go
+++ b/internal/service/rds/validate_test.go
@@ -124,6 +124,10 @@ func TestValidParamGroupName(t *testing.T) {
 		Value    string
 		ErrCount int
 	}{
+		{
+			Value:    "default.postgres9.6",
+			ErrCount: 0,
+		},
 		{
 			Value:    "tEsting123",
 			ErrCount: 1,