diff --git a/config/notifiers.go b/config/notifiers.go
index f7f627c8..ba4517e8 100644
--- a/config/notifiers.go
+++ b/config/notifiers.go
@@ -42,6 +42,14 @@ var (
 	// DefaultEmailSubject defines the default Subject header of an Email.
 	DefaultEmailSubject = `{{ template "email.default.subject" . }}`
 
+	// DefaultPagerdutyDetails defines the default values for PagerDuty details.
+	DefaultPagerdutyDetails = map[string]string{
+		"firing":       `{{ template "pagerduty.default.instances" .Alerts.Firing }}`,
+		"resolved":     `{{ template "pagerduty.default.instances" .Alerts.Resolved }}`,
+		"num_firing":   `{{ .Alerts.Firing | len }}`,
+		"num_resolved": `{{ .Alerts.Resolved | len }}`,
+	}
+
 	// DefaultPagerdutyConfig defines default values for PagerDuty configurations.
 	DefaultPagerdutyConfig = PagerdutyConfig{
 		NotifierConfig: NotifierConfig{
@@ -50,12 +58,6 @@ var (
 		Description: `{{ template "pagerduty.default.description" .}}`,
 		Client:      `{{ template "pagerduty.default.client" . }}`,
 		ClientURL:   `{{ template "pagerduty.default.clientURL" . }}`,
-		Details: map[string]string{
-			"firing":       `{{ template "pagerduty.default.instances" .Alerts.Firing }}`,
-			"resolved":     `{{ template "pagerduty.default.instances" .Alerts.Resolved }}`,
-			"num_firing":   `{{ .Alerts.Firing | len }}`,
-			"num_resolved": `{{ .Alerts.Resolved | len }}`,
-		},
 	}
 
 	// DefaultSlackConfig defines default values for Slack configurations.
@@ -217,6 +219,14 @@ func (c *PagerdutyConfig) UnmarshalYAML(unmarshal func(interface{}) error) error
 	if c.RoutingKey == "" && c.ServiceKey == "" {
 		return fmt.Errorf("missing service or routing key in PagerDuty config")
 	}
+	if c.Details == nil {
+		c.Details = make(map[string]string)
+	}
+	for k, v := range DefaultPagerdutyDetails {
+		if _, ok := c.Details[k]; !ok {
+			c.Details[k] = v
+		}
+	}
 	return nil
 }
 
diff --git a/config/notifiers_test.go b/config/notifiers_test.go
index 859337ca..c3f897f8 100644
--- a/config/notifiers_test.go
+++ b/config/notifiers_test.go
@@ -91,6 +91,63 @@ service_key: ''
 	}
 }
 
+func TestPagerdutyDetails(t *testing.T) {
+
+	var tests = []struct {
+		in      string
+		checkFn func(map[string]string)
+	}{
+		{
+			in: `
+routing_key: 'xyz'
+`,
+			checkFn: func(d map[string]string) {
+				if len(d) != 4 {
+					t.Errorf("expected 4 items, got: %d", len(d))
+				}
+			},
+		},
+		{
+			in: `
+routing_key: 'xyz'
+details:
+  key1: val1
+`,
+			checkFn: func(d map[string]string) {
+				if len(d) != 5 {
+					t.Errorf("expected 5 items, got: %d", len(d))
+				}
+			},
+		},
+		{
+			in: `
+routing_key: 'xyz'
+details:
+  key1: val1
+  key2: val2
+  firing: firing
+`,
+			checkFn: func(d map[string]string) {
+				if len(d) != 6 {
+					t.Errorf("expected 6 items, got: %d", len(d))
+				}
+			},
+		},
+	}
+	for _, tc := range tests {
+		var cfg PagerdutyConfig
+		err := yaml.UnmarshalStrict([]byte(tc.in), &cfg)
+
+		if err != nil {
+			t.Errorf("expected no error, got:%v", err)
+		}
+
+		if tc.checkFn != nil {
+			tc.checkFn(cfg.Details)
+		}
+	}
+}
+
 func TestHipchatRoomIDIsPresent(t *testing.T) {
 	in := `
 room_id: ''