diff --git a/src/win32.mak b/src/win32.mak
index ca2d2a64999e..14ed0bb18eeb 100644
--- a/src/win32.mak
+++ b/src/win32.mak
@@ -65,6 +65,9 @@ OS=windows
 
 ##### Directories
 
+# DM_HOME should be defined in the user's environment
+DM_HOME=Please_define_the__DM_HOME__environment_variable
+
 # DMC directory
 DMCROOT=$(DM_HOME)\dm
 # DMD source directories
@@ -93,6 +96,8 @@ TOOLS_DIR=..\..\tools
 CC=dmc
 # D compiler (set with env variable)
 #HOST_DC=dmd
+# For error detection:
+HOST_DC=Please_define_the__HOST_DC__environment_variable
 # Make program
 MAKE=make
 # Librarian
@@ -627,4 +632,3 @@ $G\ldfpu.obj : vcbuild\ldfpu.asm
 ############################## Generated Rules ###############################
 
 # These rules were generated by makedep, but are not currently maintained
-