diff --git a/src/db/db/dbNetlist.cc b/src/db/db/dbNetlist.cc
index 39c04268d..0d7e1cc5a 100644
--- a/src/db/db/dbNetlist.cc
+++ b/src/db/db/dbNetlist.cc
@@ -812,8 +812,12 @@ void Circuit::combine_devices ()
   tl_assert (netlist () != 0);
 
   for (Netlist::device_class_iterator dc = netlist ()->begin_device_classes (); dc != netlist ()->end_device_classes (); ++dc) {
-    combine_parallel_devices (*dc);
-    combine_serial_devices (*dc);
+    if (dc->supports_parallel_combination ()) {
+      combine_parallel_devices (*dc);
+    }
+    if (dc->supports_serial_combination ()) {
+      combine_serial_devices (*dc);
+    }
   }
 }
 
diff --git a/src/db/db/dbNetlist.h b/src/db/db/dbNetlist.h
index b3d911144..160d97634 100644
--- a/src/db/db/dbNetlist.h
+++ b/src/db/db/dbNetlist.h
@@ -1431,6 +1431,22 @@ public:
     return false;
   }
 
+  /**
+   *  @brief Returns true if the device class supports device combination in parallel mode
+   */
+  virtual bool supports_parallel_combination () const
+  {
+    return false;
+  }
+
+  /**
+   *  @brief Returns true if the device class supports device combination in serial mode
+   */
+  virtual bool supports_serial_combination () const
+  {
+    return false;
+  }
+
 private:
   friend class Netlist;
 
diff --git a/src/db/db/dbNetlistDeviceClasses.h b/src/db/db/dbNetlistDeviceClasses.h
index 76184f152..a338193f1 100644
--- a/src/db/db/dbNetlistDeviceClasses.h
+++ b/src/db/db/dbNetlistDeviceClasses.h
@@ -40,6 +40,8 @@ public:
 
   virtual void parallel (Device *a, Device *b) const = 0;
   virtual void serial (Device *a, Device *b) const = 0;
+  virtual bool supports_parallel_combination () const { return true; }
+  virtual bool supports_serial_combination () const { return true; }
 };
 
 /**
@@ -120,6 +122,7 @@ public:
   }
 
   virtual bool combine_devices (Device *a, Device *b) const;
+  virtual bool supports_parallel_combination () const { return true; }
 };
 
 /**
@@ -140,6 +143,7 @@ public:
   }
 
   virtual bool combine_devices (Device *a, Device *b) const;
+  virtual bool supports_parallel_combination () const { return true; }
 };
 
 /**
@@ -159,6 +163,7 @@ public:
   }
 
   virtual bool combine_devices (Device *a, Device *b) const;
+  virtual bool supports_parallel_combination () const { return true; }
 };
 
 }