diff --git a/make-includes/build_lecture_rules.make b/make-includes/build_lecture_rules.make
index 7c8c10b..727b267 100644
--- a/make-includes/build_lecture_rules.make
+++ b/make-includes/build_lecture_rules.make
@@ -19,7 +19,7 @@
 #
 # Standard directories.
 #
-IMGDIR=images
+IMGDIR?=images
 
 
 ################################################################################
@@ -300,6 +300,7 @@
 	@$(ECHO) "GLOBAL_HANDBOOK_INCLUDE = [$(GLOBAL_HANDBOOK_INCLUDE)]"
 	@$(ECHO) "INSTALL_DIRECTORY = [$(INSTALL_DIRECTORY)]"
 	@$(ECHO) "BUILD_DIR = [$(BUILD_DIR)]"
+	@$(ECHO) "IMGDIR = [$(IMGDIR)]"
 	@$(ECHO) "INSTALL_FILES = [$(INSTALL_FILES)]"
 	@$(ECHO) "SLIDE_IMAGES = [$(SLIDE_IMAGES)]"
 	@$(ECHO) "SLIDE_BACKGROUNDS = [$(SLIDE_BACKGROUNDS)]"