diff --git a/cde/programs/dtfile/Imakefile b/cde/programs/dtfile/Imakefile
index 51a6ad6a5..32f678655 100644
--- a/cde/programs/dtfile/Imakefile
+++ b/cde/programs/dtfile/Imakefile
@@ -35,6 +35,7 @@ EXTRA_CCOPTIONS = -xF
 
 #if defined(LinuxArchitecture)
 EXTRA_INCLUDES = -I/usr/include/freetype2
+EXTRA_DEFINES = -DFILE_MAP_OPTIMIZE
 #endif
 
 #if defined(BSDArchitecture)