diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index 41ce284157..89be6adbf5 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -17,7 +17,9 @@
 #                                                                              #
 ################################################################################
 
-cmake_minimum_required (VERSION 2.8.5)
+cmake_minimum_required(VERSION 3.1.3)
+set(CMAKE_CXX_STANDARD 11)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)  # not necessary, but encouraged
 
 project (IfcOpenShell)
 
diff --git a/src/ifcparse/IfcCharacterDecoder.cpp b/src/ifcparse/IfcCharacterDecoder.cpp
index 41638366a8..1f565d37b0 100644
--- a/src/ifcparse/IfcCharacterDecoder.cpp
+++ b/src/ifcparse/IfcCharacterDecoder.cpp
@@ -81,7 +81,7 @@ void IfcCharacterDecoder::addChar(std::stringstream& s,const UChar32& ch) {
            maximum length in bytes is 4. We add 1 for the NUL character. In other encodings
            the length could be higher, but we have not taken that into account. */
 		char extraction_buffer[5] = {};
-		UnicodeString(ch).extract(extraction_buffer,5,destination,status);
+        icu::UnicodeString(ch).extract(extraction_buffer,5,destination,status);
         extraction_buffer[4] = '\0';
 		s << extraction_buffer;
 	} else {
diff --git a/src/ifcparse/IfcCharacterDecoder.h b/src/ifcparse/IfcCharacterDecoder.h
index 39e851be0d..1bd88b969b 100644
--- a/src/ifcparse/IfcCharacterDecoder.h
+++ b/src/ifcparse/IfcCharacterDecoder.h
@@ -32,6 +32,7 @@
 
 #ifdef HAVE_ICU
 #include "unicode/ucnv.h"
+#include "unicode/unistr.h"
 #else
 typedef unsigned int UChar32;
 #endif