diff --git a/README b/README
index d6a56b050..3b0d877fa 100644
--- a/README
+++ b/README
@@ -45,6 +45,10 @@ Requirements:
 - an ANSI C compiler. This defaults to gcc. You can change this by setting
   the CC make variable.
 
+- flex and yacc.
+
+- GNU make.
+
 - about 40MB free in /tmp (or some other temporary directory).
 
 - about 6MB in the target directory.
@@ -57,14 +61,14 @@ Instructions:
 
 - Run:
 
-    make
+    make            # or gmake
 
   ...from the command line. This will do the build.
 
   The make system is fully parallelisable. If you have a multicore system,
   you probably want to do:
 
-    make -j8
+    make -j8        # or gmake -j8
 
   ...instead (substituting the right number of cores, of course). You can
   also shave a few seconds of the build time by using the -r flag.
diff --git a/lang/cem/cemcom.ansi/LLmessage.c b/lang/cem/cemcom.ansi/LLmessage.c
index 9010ce45d..c88c5eb24 100644
--- a/lang/cem/cemcom.ansi/LLmessage.c
+++ b/lang/cem/cemcom.ansi/LLmessage.c
@@ -6,6 +6,7 @@
 /*		PARSER ERROR ADMINISTRATION		*/
 
 #include	<alloc.h>
+#include	"idf.h"
 #include	"arith.h"
 #include	"LLlex.h"
 #include	"Lpars.h"
diff --git a/lang/cem/cemcom.ansi/options.c b/lang/cem/cemcom.ansi/options.c
index a8f382302..a23ff3405 100644
--- a/lang/cem/cemcom.ansi/options.c
+++ b/lang/cem/cemcom.ansi/options.c
@@ -11,6 +11,7 @@
 #include	<alloc.h>
 #include	"class.h"
 #include	"macro.h"
+#include	"idf.h"
 #include	"arith.h"
 #include	"sizes.h"
 #include	"align.h"
diff --git a/util/LLgen/build.mk b/util/LLgen/build.mk
index 3c40d1886..28da2d715 100644
--- a/util/LLgen/build.mk
+++ b/util/LLgen/build.mk
@@ -45,9 +45,9 @@ $(eval CLEANABLES += $o $1/Lpars.h)
 $o: $1/Lpars.h
 $1/Lpars.h: $2 $(LLGEN)
 	@echo LLGEN $1/Lpars.c
-	@mkdir -p $(dir $o)
+	@mkdir -p $1
 	$(hide) $(RM) $o $1/Lpars.h
-	$(hide) cd $(dir $o) && $(LLGEN) $(abspath $2)
+	$(hide) cd $1 && $(LLGEN) $(abspath $2)
 
 $(foreach f,$o,$(call cfile,$f))
 
diff --git a/util/ack/build.mk b/util/ack/build.mk
index 1b4fc146c..36e505c12 100644
--- a/util/ack/build.mk
+++ b/util/ack/build.mk
@@ -5,8 +5,8 @@ $(eval g := $(OBJDIR)/$D/dmach.c $(OBJDIR)/$D/intable.c)
 $(wordlist 2, $(words $g), $g): $(firstword $g)
 $(firstword $g): $(util-ack-mktables)
 	@echo MKTABLES
-	@mkdir -p $(dir $g)
-	$(hide) cd $(dir $g) && $(util-ack-mktables) $(INSDIR)/share
+	@mkdir -p $(OBJDIR)/$D
+	$(hide) cd $(OBJDIR)/$D && $(util-ack-mktables) $(INSDIR)/share
 
 $(eval CLEANABLES += $g)
 endef