diff --git a/pgraph/pgraph_test.go b/pgraph/pgraph_test.go
index 14b5af82..4bbe369c 100644
--- a/pgraph/pgraph_test.go
+++ b/pgraph/pgraph_test.go
@@ -764,6 +764,18 @@ Loop:
 		}
 	}
 
+	// check meta parameters
+	for v1 := range g1.Adjacency { // for each vertex in g1
+		for v2 := range g2.Adjacency { // does it match in g2 ?
+			s1, s2 := v1.Meta().Sema, v2.Meta().Sema
+			sort.Strings(s1)
+			sort.Strings(s2)
+			if !reflect.DeepEqual(s1, s2) {
+				return fmt.Errorf("vertex %s and vertex %s have different semaphores", v1.GetName(), v2.GetName())
+			}
+		}
+	}
+
 	return nil // success!
 }
 
@@ -805,7 +817,11 @@ func (ag *testGrouper) edgeMerge(e1, e2 *Edge) *Edge {
 func (g *Graph) fullPrint() (str string) {
 	str += "\n"
 	for v := range g.Adjacency {
-		str += fmt.Sprintf("* v: %v\n", v.GetName())
+		if semas := v.Meta().Sema; len(semas) > 0 {
+			str += fmt.Sprintf("* v: %v; sema: %v\n", v.GetName(), semas)
+		} else {
+			str += fmt.Sprintf("* v: %v\n", v.GetName())
+		}
 		// TODO: add explicit grouping data?
 	}
 	for v1 := range g.Adjacency {
diff --git a/pgraph/semaphore_test.go b/pgraph/semaphore_test.go
new file mode 100644
index 00000000..5212ad9b
--- /dev/null
+++ b/pgraph/semaphore_test.go
@@ -0,0 +1,93 @@
+// Mgmt
+// Copyright (C) 2013-2017+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package pgraph
+
+import (
+	"testing"
+
+	"github.com/purpleidea/mgmt/resources"
+)
+
+func NewNoopResTestSema(name string, semas []string) *NoopResTest {
+	obj := &NoopResTest{
+		NoopRes: resources.NoopRes{
+			BaseRes: resources.BaseRes{
+				Name: name,
+				MetaParams: resources.MetaParams{
+					AutoGroup: true, // always autogroup
+					Sema:      semas,
+				},
+			},
+		},
+	}
+	return obj
+}
+
+func TestPgraphSemaphoreGrouping1(t *testing.T) {
+	g1 := NewGraph("g1") // original graph
+	{
+		a1 := NewVertex(NewNoopResTestSema("a1", []string{"s:1"}))
+		a2 := NewVertex(NewNoopResTestSema("a2", []string{"s:2"}))
+		a3 := NewVertex(NewNoopResTestSema("a3", []string{"s:3"}))
+		g1.AddVertex(a1)
+		g1.AddVertex(a2)
+		g1.AddVertex(a3)
+	}
+	g2 := NewGraph("g2") // expected result
+	{
+		a123 := NewVertex(NewNoopResTestSema("a1,a2,a3", []string{"s:1", "s:2", "s:3"}))
+		g2.AddVertex(a123)
+	}
+	runGraphCmp(t, g1, g2)
+}
+
+func TestPgraphSemaphoreGrouping2(t *testing.T) {
+	g1 := NewGraph("g1") // original graph
+	{
+		a1 := NewVertex(NewNoopResTestSema("a1", []string{"s:10", "s:11"}))
+		a2 := NewVertex(NewNoopResTestSema("a2", []string{"s:2"}))
+		a3 := NewVertex(NewNoopResTestSema("a3", []string{"s:3"}))
+		g1.AddVertex(a1)
+		g1.AddVertex(a2)
+		g1.AddVertex(a3)
+	}
+	g2 := NewGraph("g2") // expected result
+	{
+		a123 := NewVertex(NewNoopResTestSema("a1,a2,a3", []string{"s:10", "s:11", "s:2", "s:3"}))
+		g2.AddVertex(a123)
+	}
+	runGraphCmp(t, g1, g2)
+}
+
+func TestPgraphSemaphoreGrouping3(t *testing.T) {
+	g1 := NewGraph("g1") // original graph
+	{
+		a1 := NewVertex(NewNoopResTestSema("a1", []string{"s:1", "s:2"}))
+		a2 := NewVertex(NewNoopResTestSema("a2", []string{"s:2"}))
+		a3 := NewVertex(NewNoopResTestSema("a3", []string{"s:3"}))
+		g1.AddVertex(a1)
+		g1.AddVertex(a2)
+		g1.AddVertex(a3)
+	}
+	g2 := NewGraph("g2") // expected result
+	{
+		a123 := NewVertex(NewNoopResTestSema("a1,a2,a3", []string{"s:1", "s:2", "s:3"}))
+		g2.AddVertex(a123)
+	}
+	runGraphCmp(t, g1, g2)
+}
diff --git a/resources/resources.go b/resources/resources.go
index aaf5e460..cd0aceee 100644
--- a/resources/resources.go
+++ b/resources/resources.go
@@ -35,6 +35,7 @@ import (
 	"github.com/purpleidea/mgmt/converger"
 	"github.com/purpleidea/mgmt/event"
 	"github.com/purpleidea/mgmt/prometheus"
+	"github.com/purpleidea/mgmt/util"
 
 	errwrap "github.com/pkg/errors"
 	"golang.org/x/time/rate"
@@ -496,6 +497,12 @@ func (obj *BaseRes) GroupRes(res Res) error {
 		return fmt.Errorf("the %v resource is already grouped", res)
 	}
 
+	// merging two resources into one should yield the sum of their semas
+	if semas := res.Meta().Sema; len(semas) > 0 {
+		obj.Meta().Sema = append(obj.Meta().Sema, semas...)
+		obj.Meta().Sema = util.StrRemoveDuplicatesInList(obj.Meta().Sema)
+	}
+
 	obj.grouped = append(obj.grouped, res)
 	res.SetGrouped(true) // i am contained _in_ a group
 	return nil
diff --git a/util/util.go b/util/util.go
index d49cafcf..298edb36 100644
--- a/util/util.go
+++ b/util/util.go
@@ -57,7 +57,7 @@ func Uint64KeyFromStrInMap(needle string, haystack map[uint64]string) (uint64, b
 }
 
 // StrRemoveDuplicatesInList removes any duplicate values in the list.
-// This is a possibly sub-optimal, O(n^2)? implementation.
+// This implementation is possibly sub-optimal (O(n^2)?) but preserves ordering.
 func StrRemoveDuplicatesInList(list []string) []string {
 	unique := []string{}
 	for _, x := range list {