diff --git a/simgear/nasal/code.c b/simgear/nasal/code.c
index 511f490f..5601b074 100644
--- a/simgear/nasal/code.c
+++ b/simgear/nasal/code.c
@@ -313,7 +313,10 @@ static struct Frame* setupFuncall(naContext ctx, int nargs, int mcall, int named
     ctx->opFrame = opf;
 
     if(IS_CCODE(code)) {
-        naRef result = (*PTR(code).ccode->fptr)(ctx, obj, nargs, args);
+        struct naCCode *ccode = PTR(code).ccode;
+        naRef result = ccode->fptru
+                     ? (*ccode->fptru)(ctx, obj, nargs, args, ccode->user_data)
+                     : (*ccode->fptr)(ctx, obj, nargs, args);
         if(named) ERR(ctx, "native functions have no named arguments");
         ctx->opTop = ctx->opFrame;
         PUSH(result);
diff --git a/simgear/nasal/data.h b/simgear/nasal/data.h
index deb4fbdc..a2c023ef 100644
--- a/simgear/nasal/data.h
+++ b/simgear/nasal/data.h
@@ -160,7 +160,15 @@ struct naFunc {
 
 struct naCCode {
     GC_HEADER;
-    naCFunction fptr;
+    union {
+        naCFunction fptr; //<! pointer to simple callback function. Invalid if
+                          //   fptru is not NULL.
+        struct {
+            void* user_data;
+            void(*destroy)(void*);
+            naCFunctionU fptru;
+        };
+    };
 };
 
 struct naGhost {
diff --git a/simgear/nasal/gc.c b/simgear/nasal/gc.c
index e9d9b7b8..9773c795 100644
--- a/simgear/nasal/gc.c
+++ b/simgear/nasal/gc.c
@@ -128,6 +128,12 @@ static void naCode_gcclean(struct naCode* o)
     naFree(o->constants);  o->constants = 0;
 }
 
+static void naCCode_gcclean(struct naCCode* c)
+{
+    if(c->fptru && c->user_data && c->destroy) c->destroy(c->user_data);
+    c->user_data = 0;
+}
+
 static void naGhost_gcclean(struct naGhost* g)
 {
     if(g->ptr && g->gtype->destroy) g->gtype->destroy(g->ptr);
@@ -142,6 +148,7 @@ static void freeelem(struct naPool* p, struct naObj* o)
     case T_VEC:   naVec_gcclean  ((struct naVec*)  o); break;
     case T_HASH:  naiGCHashClean ((struct naHash*) o); break;
     case T_CODE:  naCode_gcclean ((struct naCode*) o); break;
+    case T_CCODE: naCCode_gcclean((struct naCCode*)o); break;
     case T_GHOST: naGhost_gcclean((struct naGhost*)o); break;
     }
     p->free[p->nfree++] = o;  // ...and add it to the free list
diff --git a/simgear/nasal/misc.c b/simgear/nasal/misc.c
index dae0bfe4..a249fce7 100644
--- a/simgear/nasal/misc.c
+++ b/simgear/nasal/misc.c
@@ -107,6 +107,24 @@ naRef naNewCCode(struct Context* c, naCFunction fptr)
 {
     naRef r = naNew(c, T_CCODE);
     PTR(r).ccode->fptr = fptr;
+    PTR(r).ccode->fptru = 0;
+    return r;
+}
+
+naRef naNewCCodeU(struct Context* c, naCFunctionU fptr, void* user_data)
+{
+    return naNewCCodeUD(c, fptr, user_data, 0);
+}
+
+naRef naNewCCodeUD( struct Context* c,
+                    naCFunctionU fptr,
+                    void* user_data,
+                    void (*destroy)(void*) )
+{
+    naRef r = naNew(c, T_CCODE);
+    PTR(r).ccode->fptru = fptr;
+    PTR(r).ccode->user_data = user_data;
+    PTR(r).ccode->destroy = destroy;
     return r;
 }
 
diff --git a/simgear/nasal/nasal.h b/simgear/nasal/nasal.h
index 7fc54203..d3cb9167 100644
--- a/simgear/nasal/nasal.h
+++ b/simgear/nasal/nasal.h
@@ -16,10 +16,14 @@ extern "C" {
 #endif
 
 typedef struct Context* naContext;
-    
+
 // The function signature for an extension function:
 typedef naRef (*naCFunction)(naContext ctx, naRef me, int argc, naRef* args);
 
+// The function signature for an extension function with userdata passed back:
+typedef naRef (*naCFunctionU)
+              (naContext ctx, naRef me, int argc, naRef* args, void* user_data);
+
 // All Nasal code runs under the watch of a naContext:
 naContext naNewContext();
 void naFreeContext(naContext c);
@@ -146,7 +150,19 @@ naRef naNewString(naContext c);
 naRef naNewVector(naContext c);
 naRef naNewHash(naContext c);
 naRef naNewFunc(naContext c, naRef code);
+
+/**
+ * Register extension function
+ *
+ * @param fptr      Pointer to C-function
+ * @param user_data Optional user data passed back on calling the function
+ * @param destroy   Optional callback called if function gets freed by garbage
+ *                  collector to free user data if required.
+ */
 naRef naNewCCode(naContext c, naCFunction fptr);
+naRef naNewCCodeU(naContext c, naCFunctionU fptr, void* user_data);
+naRef naNewCCodeUD(naContext c, naCFunctionU fptr, void* user_data,
+                                                   void (*destroy)(void*));
 
 // Some useful conversion/comparison routines
 int naEqual(naRef a, naRef b) GCC_PURE;