diff --git a/build/make/Makefile.in b/build/make/Makefile.in
index 7416ea7d3d2..2856fd71ade 100644
--- a/build/make/Makefile.in
+++ b/build/make/Makefile.in
@@ -9,7 +9,7 @@
 # obscure the substance of the actual rules, this file can be debugged by
 # running:
 #
-#     $ make -f build/make/Makefile -n DEBUG_RULES=1 SAGE_PKGCONFIG=1
+#     $ make -f build/make/Makefile -n DEBUG_RULES=1
 #
 # This will not actually run any rules (the -n flag) but will print all the
 # rules generated from the templates.
@@ -17,6 +17,7 @@
 # Always use bash for make rules
 SHELL = @SHELL@
 
+ifndef DEBUG_RULES
 # Check a variable that is only set in build/make/install, but not in sage-env, for example
 ifndef SAGE_PKGCONFIG
 # Set by build/bin/sage-sdist, which invokes the Makefile directly in
@@ -25,6 +26,7 @@ ifndef SAGE_SPKG_COPY_UPSTREAM
 $(error This Makefile needs to be invoked by build/make/install)
 endif
 endif
+endif
 
 # Directory to keep track of which packages are installed - relative to installation prefix
 SPKG_INST_RELDIR = var/lib/sage/installed