diff --git a/icu4c/source/common/ustr_imp.h b/icu4c/source/common/ustr_imp.h
index 9c610f65b55..5ceba85008f 100644
--- a/icu4c/source/common/ustr_imp.h
+++ b/icu4c/source/common/ustr_imp.h
@@ -116,7 +116,7 @@ u_internalGetCombiningClass(UChar32 c);
  * Remember to use the u_releaseDefaultConverter when you are done.
  * @internal
  */
-U_CAPI UConverter*
+U_CAPI UConverter* U_EXPORT2
 u_getDefaultConverter(UErrorCode *status);
 
 
@@ -124,7 +124,23 @@ u_getDefaultConverter(UErrorCode *status);
  * Release the default converter to the converter cache.
  * @internal
  */
-U_CAPI void
+U_CAPI void U_EXPORT2
 u_releaseDefaultConverter(UConverter *converter);
 
+/**
+ * NUL-terminate a UChar * string if possible.
+ * If length  < destCapacity then NUL-terminate.
+ * If length == destCapacity then do not terminate but set U_STRING_NOT_TERMINATED_WARNING.
+ * If length  > destCapacity then do not terminate but set U_BUFFER_OVERFLOW_ERROR.
+ *
+ * @param dest Destination buffer, can be NULL if destCapacity==0.
+ * @param destCapacity Number of UChars available at dest.
+ * @param length Number of UChars that were (to be) written to dest.
+ * @param pErrorCode ICU error code.
+ * @return length
+ * @internal
+ */
+U_CAPI int32_t U_EXPORT2
+u_terminateUChars(UChar *dest, int32_t destCapacity, int32_t length, UErrorCode *pErrorCode);
+
 #endif
diff --git a/icu4c/source/common/ustring.c b/icu4c/source/common/ustring.c
index 37230672fa3..1a29f4594ca 100644
--- a/icu4c/source/common/ustring.c
+++ b/icu4c/source/common/ustring.c
@@ -1284,3 +1284,27 @@ u_growBufferFromStatic(void *context,
     *pBuffer=newBuffer;
     return (UBool)(newBuffer!=NULL);
 }
+
+/* NUL-termination of strings ----------------------------------------------- */
+
+U_CAPI int32_t U_EXPORT2
+u_terminateUChars(UChar *dest, int32_t destCapacity, int32_t length, UErrorCode *pErrorCode) {
+    if(pErrorCode==NULL || U_FAILURE(*pErrorCode)) {
+        return length;
+    }
+
+    /* not a public function, so no complete argument checking */
+
+    if(length<destCapacity) {
+        /* NUL-terminate the string, the NUL fits */
+        dest[length]=0;
+    } else if(length==destCapacity) {
+        /* unable to NUL-terminate, but the string itself fit - set a warning code */
+        *pErrorCode=U_STRING_NOT_TERMINATED_WARNING;
+    } else /* length>destCapacity */ {
+        /* even the string itself did not fit - set an error code */
+        *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+    }
+
+    return length;
+}