diff --git a/builds/posix/make.defaults b/builds/posix/make.defaults
index 94d903ddca6..2fcd0955462 100755
--- a/builds/posix/make.defaults
+++ b/builds/posix/make.defaults
@@ -101,8 +101,8 @@ GLOB_OPTIONS:=
 
 #____________________________________________________________________________
 
-# Firebird needs no RTTI, make it build with icu-75.1
-RTTI_FLAG:= -fno-rtti -DU_SHOW_CPLUSPLUS_API=0
+# Firebird needs no RTTI, make it build with icu-76.1
+RTTI_FLAG:= -fno-rtti -DU_SHOW_CPLUSPLUS_API=0 -DU_SHOW_CPLUSPLUS_HEADER_API=0
 
 # If this is defined then we use special rules useful for developers only
 IsDeveloper = @DEVEL_FLG@