diff --git a/ext/win32ole/win32ole.c b/ext/win32ole/win32ole.c
index cabbeb8..71c4f7f 100644
--- a/ext/win32ole/win32ole.c
+++ b/ext/win32ole/win32ole.c
@@ -929,7 +929,13 @@ ole_mb2wc(char *pm, int len, UINT cp)
 #endif
     }
     size = MultiByteToWideChar(cp, 0, pm, len, NULL, 0);
+    if (!size) {
+        ole_raise(HRESULT_LASTERROR(), eWIN32OLERuntimeError, "fail to convert CP%d to Unicode", cp);
+    }
     pw = SysAllocStringLen(NULL, size);
+    if (!pw) {
+        ole_raise(HRESULT_LASTERROR(), eWIN32OLERuntimeError, "fail to allocate Unicode string");
+    }
     pw[size-1] = 0;
     MultiByteToWideChar(cp, 0, pm, len, pw, size);
     return pw;
diff --git a/ext/win32ole/win32ole_error.h b/ext/win32ole/win32ole_error.h
index a2f3298..01f18d1 100644
--- a/ext/win32ole/win32ole_error.h
+++ b/ext/win32ole/win32ole_error.h
@@ -6,4 +6,6 @@ extern VALUE eWIN32OLEQueryInterfaceError;
 NORETURN(PRINTF_ARGS(void ole_raise(HRESULT hr, VALUE ecs, const char *fmt, ...), 3, 4));
 void Init_win32ole_error(void);
 
+#define HRESULT_LASTERROR() HRESULT_FROM_WIN32(GetLastError())
+
 #endif
diff --git a/test/win32ole/test_win32ole.rb b/test/win32ole/test_win32ole.rb
index e6347e8..55a3127 100644
--- a/test/win32ole/test_win32ole.rb
+++ b/test/win32ole/test_win32ole.rb
@@ -519,6 +519,15 @@ def test_method_missing
       assert_raise(ArgumentError) {@dict1.method_missing("foo=")}
       assert_raise(ArgumentError) {@dict1.method_missing("foo=", 1, 2)}
     end
+
+    def test_invoke_with_too_long_string
+      skip = ENV["WIN32OLE_MEMORY_INTENSIVE_TESTS"]
+      return unless skip
+      omit "This test creates a 1GiB string" unless skip == "yes"
+      str = "a" * 0x40000000
+      assert_raise(WIN32OLE::RuntimeError) {@dict1.invoke(str)}
+      assert_raise(WIN32OLE::RuntimeError) {@dict2.invoke(str)}
+    end
   end
 
   # test of subclass of WIN32OLE