diff --git a/icu4c/source/common/charstr.cpp b/icu4c/source/common/charstr.cpp
index 76723d9790c..846a074feb6 100644
--- a/icu4c/source/common/charstr.cpp
+++ b/icu4c/source/common/charstr.cpp
@@ -1,6 +1,6 @@
 /*
 *******************************************************************************
-*   Copyright (C) 2010-2011, International Business Machines
+*   Copyright (C) 2010-2015, International Business Machines
 *   Corporation and others.  All Rights Reserved.
 *******************************************************************************
 *   file name:  charstr.cpp
@@ -16,6 +16,7 @@
 #include "charstr.h"
 #include "cmemory.h"
 #include "cstring.h"
+#include "uinvchar.h"
 
 U_NAMESPACE_BEGIN
 
@@ -101,6 +102,13 @@ char *CharString::getAppendBuffer(int32_t minCapacity,
 }
 
 CharString &CharString::appendInvariantChars(const UnicodeString &s, UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) {
+        return *this;
+    }
+    if (!uprv_isInvariantUString(s.getBuffer(), s.length())) {
+        errorCode = U_INVARIANT_CONVERSION_ERROR;
+        return *this;
+    }
     if(ensureCapacity(len+s.length()+1, 0, errorCode)) {
         len+=s.extract(0, 0x7fffffff, buffer.getAlias()+len, buffer.getCapacity()-len, US_INV);
     }
diff --git a/icu4c/source/test/intltest/strtest.cpp b/icu4c/source/test/intltest/strtest.cpp
index 2081454d5fe..5075fa5fc8e 100644
--- a/icu4c/source/test/intltest/strtest.cpp
+++ b/icu4c/source/test/intltest/strtest.cpp
@@ -1,6 +1,6 @@
 /********************************************************************
  * COPYRIGHT: 
- * Copyright (c) 1997-2012, International Business Machines Corporation and
+ * Copyright (c) 1997-2015, International Business Machines Corporation and
  * others. All Rights Reserved.
  ********************************************************************/
 /*   file name:  strtest.cpp
@@ -521,4 +521,14 @@ StringTest::TestCharString() {
     if (0 != strcmp(expected, chStr.data()) || (int32_t)strlen(expected) != chStr.length()) {
         errln("CharString.getAppendBuffer().append(**) failed.");
     }
+
+    UErrorCode ec = U_ZERO_ERROR;
+    chStr.clear();
+    chStr.appendInvariantChars(UnicodeString("The '@' character is not invariant."), ec);
+    if (ec != U_INVARIANT_CONVERSION_ERROR) {
+        errln("%s:%d expected U_INVARIANT_CONVERSION_ERROR, got %s", __FILE__, __LINE__, u_errorName(ec));
+    }
+    if (chStr.length() != 0) {
+        errln("%s:%d expected length() = 0, got %d", __FILE__, __LINE__, chStr.length());
+    }
 }