Index: BUILD.txt
==================================================================
--- BUILD.txt
+++ BUILD.txt
@@ -4,15 +4,18 @@
 
 If you have an unusual unix system for which the standard Makefile
 will not work, or if you want to do some non-standard options, you can
 also run:
 
-   ./configure; make
+   ./configure; make -f GNUmakefile
 
 The ./configure script builds GNUmakefile which will be used in place
 of Makefile.  Run "./configure --help" for a listing of the available
 options.
+
+You must explicitly specify that make should use GNUmakefile in case
+your platform does not use GNU make.
 
 On a windows box, use one of the Makefiles in the win/ subdirectory,
 according to your compiler and environment.  If you have GCC and MSYS
 installed on your system, the consider:
 

Index: GNUmakefile.in
==================================================================
--- GNUmakefile.in
+++ GNUmakefile.in
@@ -37,9 +37,12 @@
 LIB =	@LDFLAGS@ @EXTRA_LDFLAGS@ @LIBS@
 TCC +=	@EXTRA_CFLAGS@ @CPPFLAGS@ @CFLAGS@ -DHAVE_AUTOCONFIG_H
 INSTALLDIR = $(DESTDIR)@prefix@/bin
 USE_SYSTEM_SQLITE = @USE_SYSTEM_SQLITE@
 
+# Disable the platform check
+PLATFORM_CHECK_KIND = disable
+
 include $(SRCDIR)/main.mk
 
 distclean: clean
 	rm -f autoconfig.h config.log GNUmakefile

Index: Makefile
==================================================================
--- Makefile
+++ Makefile
@@ -70,6 +70,9 @@
 TCC.FreeBSD += -DUSE_PREAD
 TCC.NetBSD += -DUSE_PREAD
 TCC.OpenBSD += -DUSE_PREAD
 TCC += $(TCC.$(HOST_OS))
 
+# Platform check
+PLATFORM_CHECK_KIND = Makefile
+
 include $(SRCDIR)/main.mk

ADDED   src/check-platform.sh
Index: src/check-platform.sh
==================================================================
--- /dev/null
+++ src/check-platform.sh
@@ -0,0 +1,26 @@
+#!/bin/sh
+
+# This script checks that the default makefile is only used on platforms where it is
+# positively known to work.
+#
+# Building on other platforms can result in subtly broken binaries.
+
+HOST_OS=`uname -s`
+
+# Check host OS, or whether this check has been disabled because we're running through
+# the autosetup GNUmakefile.
+if [ $HOST_OS == Linux ] || [ $HOST_OS == Darwin ] || [ X$1 == Xdisable ]
+then
+    touch bld/checked-platform.$1
+else
+    echo
+    echo The default Makefile cannot be used on this platform.
+    echo
+    echo Use
+    echo
+    echo "   ./configure; make -f GNUmakefile"
+    echo
+    echo to build fossil.
+    echo
+    exit 1
+fi

Index: src/main.mk
==================================================================
--- src/main.mk
+++ src/main.mk
@@ -303,11 +303,14 @@
 SQLITE3_OBJ.0 = $(OBJDIR)/sqlite3.o
 SQLITE3_OBJ.  = $(SQLITE3_OBJ.0)
 
 EXTRAOBJ =  $(SQLITE3_OBJ.$(USE_SYSTEM_SQLITE))  $(OBJDIR)/shell.o  $(OBJDIR)/th.o  $(OBJDIR)/th_lang.o
 
-$(APPNAME):	$(OBJDIR)/headers $(OBJ) $(EXTRAOBJ)
+$(OBJDIR)/checked-platform.$(PLATFORM_CHECK_KIND):	$(SRCDIR)/check-platform.sh
+	sh $(SRCDIR)/check-platform.sh $(PLATFORM_CHECK_KIND)
+
+$(APPNAME):	$(OBJDIR)/checked-platform.$(PLATFORM_CHECK_KIND) $(OBJDIR)/headers $(OBJ) $(EXTRAOBJ)
 	$(TCC) -o $(APPNAME) $(OBJ) $(EXTRAOBJ) $(LIB)
 
 # This rule prevents make from using its default rules to try build
 # an executable named "manifest" out of the file named "manifest.c"
 #

Index: src/makemake.tcl
==================================================================
--- src/makemake.tcl
+++ src/makemake.tcl
@@ -204,11 +204,14 @@
   $(SQLITE3_OBJ.$(USE_SYSTEM_SQLITE)) \
   $(OBJDIR)/shell.o \
   $(OBJDIR)/th.o \
   $(OBJDIR)/th_lang.o
 
-$(APPNAME):	$(OBJDIR)/headers $(OBJ) $(EXTRAOBJ)
+$(OBJDIR)/checked-platform.$(PLATFORM_CHECK_KIND):	$(SRCDIR)/check-platform.sh
+	sh $(SRCDIR)/check-platform.sh $(PLATFORM_CHECK_KIND)
+
+$(APPNAME):	$(OBJDIR)/checked-platform.$(PLATFORM_CHECK_KIND) $(OBJDIR)/headers $(OBJ) $(EXTRAOBJ)
 	$(TCC) -o $(APPNAME) $(OBJ) $(EXTRAOBJ) $(LIB)
 
 # This rule prevents make from using its default rules to try build
 # an executable named "manifest" out of the file named "manifest.c"
 #