diff --git a/AUTHORS b/AUTHORS
index 0367593c..de37a7b8 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -26,4 +26,6 @@ Charlotte Koch <cfkoch@edgebsd.org>
 Michel Hermier <michel.hermier@gmail.com>
 Taylor Hoff <primdevs@gmail.com>
 ruby0x1 <ruby0x1@pm.me>
+Kolja Kube <code@koljaku.be>
 Alexander Klingenbeck <alexander.klingenbeck@gmx.de>
+
diff --git a/doc/site/embedding/configuring-the-vm.markdown b/doc/site/embedding/configuring-the-vm.markdown
index 39b6f425..9ea68a34 100644
--- a/doc/site/embedding/configuring-the-vm.markdown
+++ b/doc/site/embedding/configuring-the-vm.markdown
@@ -182,7 +182,7 @@ These fields control how the VM allocates and manages memory.
 This lets you provide a custom memory allocation function. Its signature is:
 
 <pre class="snippet" data-lang="c">
-void* reallocate(void* memory, size_t newSize)
+void* reallocate(void* memory, size_t newSize, void* userData)
 </pre>
 
 Wren uses this one function to allocate, grow, shrink, and deallocate memory.
diff --git a/src/include/wren.h b/src/include/wren.h
index 0dddc430..69fa1099 100644
--- a/src/include/wren.h
+++ b/src/include/wren.h
@@ -47,7 +47,7 @@ typedef struct WrenHandle WrenHandle;
 //
 // - To free memory, [memory] will be the memory to free and [newSize] will be
 //   zero. It should return NULL.
-typedef void* (*WrenReallocateFn)(void* memory, size_t newSize);
+typedef void* (*WrenReallocateFn)(void* memory, size_t newSize, void* userData);
 
 // A function callable from Wren code, but implemented in C.
 typedef void (*WrenForeignMethodFn)(WrenVM* vm);
diff --git a/src/vm/wren_value.c b/src/vm/wren_value.c
index 705987c8..d475b88b 100644
--- a/src/vm/wren_value.c
+++ b/src/vm/wren_value.c
@@ -975,7 +975,8 @@ void wrenGrayObj(WrenVM* vm, Obj* obj)
   {
     vm->grayCapacity = vm->grayCount * 2;
     vm->gray = (Obj**)vm->config.reallocateFn(vm->gray,
-                                              vm->grayCapacity * sizeof(Obj*));
+                                              vm->grayCapacity * sizeof(Obj*),
+                                              vm->config.userData);
   }
 
   vm->gray[vm->grayCount++] = obj;
diff --git a/src/vm/wren_vm.c b/src/vm/wren_vm.c
index b77a1216..a63f973e 100644
--- a/src/vm/wren_vm.c
+++ b/src/vm/wren_vm.c
@@ -25,7 +25,7 @@
 // may return a non-NULL pointer which must not be dereferenced but nevertheless
 // should be freed. To prevent that, we avoid calling realloc() with a zero
 // size.
-static void* defaultReallocate(void* ptr, size_t newSize)
+static void* defaultReallocate(void* ptr, size_t newSize, void* _)
 {
   if (newSize == 0)
   {
@@ -54,9 +54,13 @@ void wrenInitConfiguration(WrenConfiguration* config)
 WrenVM* wrenNewVM(WrenConfiguration* config)
 {
   WrenReallocateFn reallocate = defaultReallocate;
-  if (config != NULL) reallocate = config->reallocateFn;
+  void* userData = NULL;
+  if (config != NULL) {
+    reallocate = config->reallocateFn;
+    userData = config->userData;
+  }
   
-  WrenVM* vm = (WrenVM*)reallocate(NULL, sizeof(*vm));
+  WrenVM* vm = (WrenVM*)reallocate(NULL, sizeof(*vm), userData);
   memset(vm, 0, sizeof(WrenVM));
 
   // Copy the configuration if given one.
@@ -73,7 +77,7 @@ WrenVM* wrenNewVM(WrenConfiguration* config)
   vm->grayCount = 0;
   // TODO: Tune this.
   vm->grayCapacity = 4;
-  vm->gray = (Obj**)reallocate(NULL, vm->grayCapacity * sizeof(Obj*));
+  vm->gray = (Obj**)reallocate(NULL, vm->grayCapacity * sizeof(Obj*), userData);
   vm->nextGC = vm->config.initialHeapSize;
 
   wrenSymbolTableInit(&vm->methodNames);
@@ -97,7 +101,7 @@ void wrenFreeVM(WrenVM* vm)
   }
 
   // Free up the GC gray set.
-  vm->gray = (Obj**)vm->config.reallocateFn(vm->gray, 0);
+  vm->gray = (Obj**)vm->config.reallocateFn(vm->gray, 0, vm->config.userData);
 
   // Tell the user if they didn't free any handles. We don't want to just free
   // them here because the host app may still have pointers to them that they
@@ -220,7 +224,7 @@ void* wrenReallocate(WrenVM* vm, void* memory, size_t oldSize, size_t newSize)
   if (newSize > 0 && vm->bytesAllocated > vm->nextGC) wrenCollectGarbage(vm);
 #endif
 
-  return vm->config.reallocateFn(memory, newSize);
+  return vm->config.reallocateFn(memory, newSize, vm->config.userData);
 }
 
 // Captures the local variable [local] into an [Upvalue]. If that local is
diff --git a/test/api/user_data.c b/test/api/user_data.c
index 676fddf5..7c1a426d 100644
--- a/test/api/user_data.c
+++ b/test/api/user_data.c
@@ -5,6 +5,18 @@
 static const char* data = "my user data";
 static const char* otherData = "other user data";
 
+void* testReallocateFn(void* ptr, size_t newSize, void* userData) {
+  if (strcmp(userData, data) != 0) return NULL;
+
+  if (newSize == 0)
+  {
+    free(ptr);
+    return NULL;
+  }
+
+  return realloc(ptr, newSize);
+}
+
 static void test(WrenVM* vm)
 {
   WrenConfiguration configuration;
@@ -17,6 +29,7 @@ static void test(WrenVM* vm)
     return;
   }
 
+  configuration.reallocateFn = testReallocateFn;
   configuration.userData = (void*)data;
 
   WrenVM* otherVM = wrenNewVM(&configuration);