diff --git a/components.go b/components.go
index 7c808b3..71d4e96 100644
--- a/components.go
+++ b/components.go
@@ -238,7 +238,11 @@ func (cb *ComponentBase) SetURL(s string, props ...PropertyParameter) {
 }
 
 func (cb *ComponentBase) SetOrganizer(s string, props ...PropertyParameter) {
-	cb.SetProperty(ComponentPropertyOrganizer, "mailto:"+s, props...)
+	if !strings.HasPrefix(s, "mailto:") {
+		s = "mailto:" + s
+	}
+
+	cb.SetProperty(ComponentPropertyOrganizer, s, props...)
 }
 
 func (cb *ComponentBase) SetColor(s string, props ...PropertyParameter) {
@@ -258,7 +262,11 @@ func (cb *ComponentBase) setResources(r string, props ...PropertyParameter) {
 }
 
 func (cb *ComponentBase) AddAttendee(s string, props ...PropertyParameter) {
-	cb.AddProperty(ComponentPropertyAttendee, "mailto:"+s, props...)
+	if !strings.HasPrefix(s, "mailto:") {
+		s = "mailto:" + s
+	}
+
+	cb.AddProperty(ComponentPropertyAttendee, s, props...)
 }
 
 func (cb *ComponentBase) AddExdate(s string, props ...PropertyParameter) {
diff --git a/components_test.go b/components_test.go
index d42a83e..bb38585 100644
--- a/components_test.go
+++ b/components_test.go
@@ -108,3 +108,27 @@ func TestGetLastModifiedAt(t *testing.T) {
 		t.Errorf("got last modified = %q, want %q", got, lastModified)
 	}
 }
+
+func TestSetMailtoPrefix(t *testing.T) {
+	e := NewEvent("test-set-organizer")
+
+	e.SetOrganizer("org1@provider.com")
+	if !strings.Contains(e.Serialize(), "ORGANIZER:mailto:org1@provider.com") {
+		t.Errorf("expected single mailto: prefix for email org1")
+	}
+
+	e.SetOrganizer("mailto:org2@provider.com")
+	if !strings.Contains(e.Serialize(), "ORGANIZER:mailto:org2@provider.com") {
+		t.Errorf("expected single mailto: prefix for email org2")
+	}
+
+	e.AddAttendee("att1@provider.com")
+	if !strings.Contains(e.Serialize(), "ATTENDEE:mailto:att1@provider.com") {
+		t.Errorf("expected single mailto: prefix for email att1")
+	}
+
+	e.AddAttendee("mailto:att2@provider.com")
+	if !strings.Contains(e.Serialize(), "ATTENDEE:mailto:att2@provider.com") {
+		t.Errorf("expected single mailto: prefix for email att2")
+	}
+}