diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 0cd366503..b6d4b35cd 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -44,7 +44,7 @@ set (task_SRCS A3.cpp A3.h
                text.cpp text.h
                utf8.cpp utf8.h
                util.cpp util.h
-               wcwidth6.c)
+               wcwidth6.cpp)
 
 add_library (task STATIC ${task_SRCS})
 add_executable (task_executable main.cpp)
diff --git a/src/text.cpp b/src/text.cpp
index 6713490a4..aff701ab8 100644
--- a/src/text.cpp
+++ b/src/text.cpp
@@ -48,7 +48,6 @@ static const char* newline = "\n";
 static const char* noline  = "";
 
 static void replace_positional (std::string&, const std::string&, const std::string&);
-extern "C" int mk_wcwidth (wchar_t);
 
 ///////////////////////////////////////////////////////////////////////////////
 void wrapText (
diff --git a/src/text.h b/src/text.h
index 1127c8063..cf90dbfc0 100644
--- a/src/text.h
+++ b/src/text.h
@@ -91,5 +91,7 @@ std::string rightJustifyZero (const int, const int);
 std::string rightJustify (const int, const int);
 std::string rightJustify (const std::string&, const int);
 
+int mk_wcwidth (wchar_t);
+
 #endif
 ////////////////////////////////////////////////////////////////////////////////
diff --git a/src/wcwidth6.c b/src/wcwidth6.cpp
similarity index 100%
rename from src/wcwidth6.c
rename to src/wcwidth6.cpp