diff --git a/icu4c/source/tools/gennorm2/gennorm2.cpp b/icu4c/source/tools/gennorm2/gennorm2.cpp
index a15dd689c399..49184703d0a6 100644
--- a/icu4c/source/tools/gennorm2/gennorm2.cpp
+++ b/icu4c/source/tools/gennorm2/gennorm2.cpp
@@ -78,8 +78,11 @@ static UOption options[]={
     UOPTION_DEF("fast", '\1', UOPT_NO_ARG)
 };
 
-extern "C" int
+U_NAMESPACE_END
+
+int
 main(int argc, char* argv[]) {
+    U_NAMESPACE_USE
     U_MAIN_INIT_ARGS(argc, argv);
 
     /* preset then read command line options */
@@ -228,6 +231,8 @@ main(int argc, char* argv[]) {
 #endif
 }
 
+U_NAMESPACE_BEGIN
+
 #if !UCONFIG_NO_NORMALIZATION
 
 void parseFile(std::ifstream &f, Normalizer2DataBuilder &builder) {