diff --git a/ChangeLog b/ChangeLog
index 52d70866..9b8e1e5d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -9,6 +9,11 @@
 
 	* builds/unix/install.mk (install): Fix path for ftmodule.h.
 
+	* Makefile, *.mk: Use `?=' where appropriate.
+
+	* builds/detect.mk (TOP_DIR), builds/os2/os2-dev.mk (TOP_DIR),
+	builds/win32/w32-dev.mk (TOP_DIR): Removed.  Defined elsewhere.
+
 2006-01-31  Werner Lemberg  <wl@gnu.org>
 
 	Implement new, simplified module selection.  With GNU make it is now
diff --git a/Makefile b/Makefile
index ab8dba59..c1fa16ce 100644
--- a/Makefile
+++ b/Makefile
@@ -15,22 +15,18 @@
 
 # Project names
 #
-PROJECT := freetype
+PROJECT       := freetype
 PROJECT_TITLE := FreeType
 
 # The variable TOP_DIR holds the path to the topmost directory in the project
 # engine source hierarchy.  If it is not defined, default it to `.'.
 #
-ifndef TOP_DIR
-  TOP_DIR := .
-endif
+TOP_DIR ?= .
 
 # The variable OBJ_DIR gives the location where object files and the
 # FreeType library are built.
 #
-ifndef OBJ_DIR
-  OBJ_DIR := $(TOP_DIR)/objs
-endif
+OBJ_DIR ?= $(TOP_DIR)/objs
 
 
 include $(TOP_DIR)/builds/toplevel.mk
diff --git a/builds/ansi/ansi-def.mk b/builds/ansi/ansi-def.mk
index b4564399..6b8ecfab 100644
--- a/builds/ansi/ansi-def.mk
+++ b/builds/ansi/ansi-def.mk
@@ -63,9 +63,7 @@ T := -o$(space)
 #   Use the ANSIFLAGS variable to define the compiler flags used to enfore
 #   ANSI compliance.
 #
-ifndef CFLAGS
-  CFLAGS := -c
-endif
+CFLAGS ?= -c
 
 # ANSIFLAGS: Put there the flags used to make your compiler ANSI-compliant.
 #
diff --git a/builds/beos/beos-def.mk b/builds/beos/beos-def.mk
index c987410e..7e79d043 100644
--- a/builds/beos/beos-def.mk
+++ b/builds/beos/beos-def.mk
@@ -65,9 +65,7 @@ T := -o$(space)
 #   Use the ANSIFLAGS variable to define the compiler flags used to enfore
 #   ANSI compliance.
 #
-ifndef CFLAGS
-  CFLAGS := -c
-endif
+CFLAGS ?= -c
 
 # ANSIFLAGS: Put there the flags used to make your compiler ANSI-compliant.
 #
diff --git a/builds/compiler/ansi-cc.mk b/builds/compiler/ansi-cc.mk
index c52c12fc..3b668e20 100644
--- a/builds/compiler/ansi-cc.mk
+++ b/builds/compiler/ansi-cc.mk
@@ -3,7 +3,7 @@
 #
 
 
-# Copyright 1996-2000, 2003 by
+# Copyright 1996-2000, 2003, 2006 by
 # David Turner, Robert Wilhelm, and Werner Lemberg.
 #
 # This file is part of the FreeType project, and may only be used, modified,
@@ -62,9 +62,7 @@ T := -o$(space)
 #   Use the ANSIFLAGS variable to define the compiler flags used to enfore
 #   ANSI compliance.
 #
-ifndef CFLAGS
-  CFLAGS := -c
-endif
+CFLAGS ?= -c
 
 # ANSIFLAGS: Put there the flags used to make your compiler ANSI-compliant.
 #
@@ -75,10 +73,8 @@ ANSIFLAGS :=
 
 # Library linking
 #
-ifndef CLEAN_LIBRARY
-  CLEAN_LIBRARY = $(DELETE) $(subst /,$(SEP),$(PROJECT_LIBRARY))
-endif
-LINK_LIBRARY = $(AR) -r $@ $(subst /,$(COMPILER_SEP),$(OBJECTS_LIST))
+CLEAN_LIBRARY ?= $(DELETE) $(subst /,$(SEP),$(PROJECT_LIBRARY))
+LINK_LIBRARY   = $(AR) -r $@ $(subst /,$(COMPILER_SEP),$(OBJECTS_LIST))
 
 
 # EOF
diff --git a/builds/compiler/bcc-dev.mk b/builds/compiler/bcc-dev.mk
index 446fd4e6..ba1a88a3 100644
--- a/builds/compiler/bcc-dev.mk
+++ b/builds/compiler/bcc-dev.mk
@@ -3,7 +3,7 @@
 #
 
 
-# Copyright 1996-2000, 2003 by
+# Copyright 1996-2000, 2003, 2006 by
 # David Turner, Robert Wilhelm, and Werner Lemberg.
 #
 # This file is part of the FreeType project, and may only be used, modified,
@@ -62,9 +62,7 @@ T := -o
 #   Use the ANSIFLAGS variable to define the compiler flags used to enfore
 #   ANSI compliance.
 #
-ifndef CFLAGS
-  CFLAGS := -q -c -y -d -v -Od -w-par -w-ccc -w-rch -w-pro -w-aus
-endif
+CFLAGS ?= -q -c -y -d -v -Od -w-par -w-ccc -w-rch -w-pro -w-aus
 
 # ANSIFLAGS: Put there the flags used to make your compiler ANSI-compliant.
 #
@@ -73,10 +71,8 @@ ANSIFLAGS := -A
 
 # Library linking
 #
-ifndef CLEAN_LIBRARY
-  CLEAN_LIBRARY = $(DELETE) $(subst /,$(SEP),$(PROJECT_LIBRARY))
-endif
-LINK_LIBRARY = tlib /u $(subst /,$(COMPILER_SEP),$@ $(OBJECTS_LIST:%=+%))
+CLEAN_LIBRARY ?= $(DELETE) $(subst /,$(SEP),$(PROJECT_LIBRARY))
+LINK_LIBRARY   = tlib /u $(subst /,$(COMPILER_SEP),$@ $(OBJECTS_LIST:%=+%))
 
 
 # EOF
diff --git a/builds/compiler/bcc.mk b/builds/compiler/bcc.mk
index eedfa10f..509cb724 100644
--- a/builds/compiler/bcc.mk
+++ b/builds/compiler/bcc.mk
@@ -3,7 +3,7 @@
 #
 
 
-# Copyright 1996-2000, 2003 by
+# Copyright 1996-2000, 2003, 2006 by
 # David Turner, Robert Wilhelm, and Werner Lemberg.
 #
 # This file is part of the FreeType project, and may only be used, modified,
@@ -62,9 +62,7 @@ T := -o
 #   Use the ANSIFLAGS variable to define the compiler flags used to enfore
 #   ANSI compliance.
 #
-ifndef CFLAGS
-  CFLAGS := -c -q -y -d -v -Od -w-par -w-ccc -w-rch -w-pro -w-aus
-endif
+CFLAGS ?= -c -q -y -d -v -Od -w-par -w-ccc -w-rch -w-pro -w-aus
 
 # ANSIFLAGS: Put there the flags used to make your compiler ANSI-compliant.
 #
@@ -73,10 +71,8 @@ ANSIFLAGS := -A
 
 # Library linking
 #
-ifndef CLEAN_LIBRARY
-  CLEAN_LIBRARY = $(DELETE) $(subst /,$(SEP),$(PROJECT_LIBRARY))
-endif
-LINK_LIBRARY = tlib /u $(subst /,$(COMPILER_SEP),$@ $(OBJECTS_LIST:%=+%))
+CLEAN_LIBRARY ?= $(DELETE) $(subst /,$(SEP),$(PROJECT_LIBRARY))
+LINK_LIBRARY   = tlib /u $(subst /,$(COMPILER_SEP),$@ $(OBJECTS_LIST:%=+%))
 
 
 # EOF
diff --git a/builds/compiler/emx.mk b/builds/compiler/emx.mk
index f2be13ca..c237005c 100644
--- a/builds/compiler/emx.mk
+++ b/builds/compiler/emx.mk
@@ -3,7 +3,7 @@
 #
 
 
-# Copyright 2003 by
+# Copyright 2003, 2006 by
 # David Turner, Robert Wilhelm, and Werner Lemberg.
 #
 # This file is part of the FreeType project, and may only be used, modified,
@@ -61,9 +61,7 @@ T := -o$(space)
 #   Use the ANSIFLAGS variable to define the compiler flags used to enfore
 #   ANSI compliance.
 #
-ifndef CFLAGS
-  CFLAGS := -c -g -O6 -Wall
-endif
+CFLAGS ?= -c -g -O6 -Wall
 
 # ANSIFLAGS: Put there the flags used to make your compiler ANSI-compliant.
 #
@@ -72,10 +70,8 @@ ANSIFLAGS :=
 
 # Library linking
 #
-ifndef CLEAN_LIBRARY
-  CLEAN_LIBRARY = $(DELETE) $(subst /,$(SEP),$(PROJECT_LIBRARY))
-endif
-LINK_LIBRARY = $(foreach m,$(OBJECTS_LIST),$(AR) -r $@ $(m);) echo > nul
+CLEAN_LIBRARY ?= $(DELETE) $(subst /,$(SEP),$(PROJECT_LIBRARY))
+LINK_LIBRARY   = $(foreach m,$(OBJECTS_LIST),$(AR) -r $@ $(m);) echo > nul
 
 
 # EOF
diff --git a/builds/compiler/gcc-dev.mk b/builds/compiler/gcc-dev.mk
index c70f1173..7e96c3ef 100644
--- a/builds/compiler/gcc-dev.mk
+++ b/builds/compiler/gcc-dev.mk
@@ -3,7 +3,7 @@
 #
 
 
-# Copyright 1996-2000, 2003, 2004, 2005 by
+# Copyright 1996-2000, 2003, 2004, 2005, 2006 by
 # David Turner, Robert Wilhelm, and Werner Lemberg.
 #
 # This file is part of the FreeType project, and may only be used, modified,
@@ -87,10 +87,8 @@ ANSIFLAGS := -ansi -pedantic
 
 # Library linking
 #
-ifndef CLEAN_LIBRARY
-  CLEAN_LIBRARY = $(DELETE) $(subst /,$(SEP),$(PROJECT_LIBRARY))
-endif
-LINK_LIBRARY = $(AR) -r $@ $(OBJECTS_LIST)
+CLEAN_LIBRARY ?= $(DELETE) $(subst /,$(SEP),$(PROJECT_LIBRARY))
+LINK_LIBRARY   = $(AR) -r $@ $(OBJECTS_LIST)
 
 
 # EOF
diff --git a/builds/compiler/gcc.mk b/builds/compiler/gcc.mk
index f4c5f96f..e941443a 100644
--- a/builds/compiler/gcc.mk
+++ b/builds/compiler/gcc.mk
@@ -3,7 +3,7 @@
 #
 
 
-# Copyright 1996-2000, 2003, 2005 by
+# Copyright 1996-2000, 2003, 2005, 2006 by
 # David Turner, Robert Wilhelm, and Werner Lemberg.
 #
 # This file is part of the FreeType project, and may only be used, modified,
@@ -61,9 +61,7 @@ T := -o$(space)
 #   Use the ANSIFLAGS variable to define the compiler flags used to enfore
 #   ANSI compliance.
 #
-ifndef CFLAGS
-  CFLAGS := -c -g -O6 -Wall
-endif
+CFLAGS ?= -c -g -O6 -Wall
 
 # ANSIFLAGS: Put there the flags used to make your compiler ANSI-compliant.
 #
@@ -72,10 +70,8 @@ ANSIFLAGS := -ansi -pedantic
 
 # Library linking
 #
-ifndef CLEAN_LIBRARY
-  CLEAN_LIBRARY = $(DELETE) $(subst /,$(SEP),$(PROJECT_LIBRARY))
-endif
-LINK_LIBRARY = $(AR) -r $@ $(OBJECTS_LIST)
+CLEAN_LIBRARY ?= $(DELETE) $(subst /,$(SEP),$(PROJECT_LIBRARY))
+LINK_LIBRARY   = $(AR) -r $@ $(OBJECTS_LIST)
 
 
 # EOF
diff --git a/builds/compiler/intelc.mk b/builds/compiler/intelc.mk
index 954dcf64..24f2995b 100644
--- a/builds/compiler/intelc.mk
+++ b/builds/compiler/intelc.mk
@@ -3,7 +3,7 @@
 #
 
 
-# Copyright 1996-2000, 2003 by
+# Copyright 1996-2000, 2003, 2006 by
 # David Turner, Robert Wilhelm, and Werner Lemberg.
 #
 # This file is part of the FreeType project, and may only be used, modified,
@@ -69,9 +69,7 @@ T := /Fo
 #   _does_ compute an arithmetic value, so we disable this warning
 #   with "/Qwd32".
 #
-ifndef CFLAGS
-  CFLAGS := /nologo /c /Ox /G5 /W3 /Qwd32
-endif
+CFLAGS ?= /nologo /c /Ox /G5 /W3 /Qwd32
 
 # ANSIFLAGS: Put there the flags used to make your compiler ANSI-compliant.
 #
diff --git a/builds/compiler/unix-lcc.mk b/builds/compiler/unix-lcc.mk
index cf4ef5a0..d79f5084 100644
--- a/builds/compiler/unix-lcc.mk
+++ b/builds/compiler/unix-lcc.mk
@@ -3,7 +3,7 @@
 #
 
 
-# Copyright 1996-2000, 2003 by
+# Copyright 1996-2000, 2003, 2006 by
 # David Turner, Robert Wilhelm, and Werner Lemberg.
 #
 # This file is part of the FreeType project, and may only be used, modified,
@@ -63,9 +63,7 @@ T := -o$(space)
 #   Use the ANSIFLAGS variable to define the compiler flags used to enfore
 #   ANSI compliance.
 #
-ifndef CFLAGS
-  CFLAGS := -c -g
-endif
+CFLAGS ?= -c -g
 
 # ANSIFLAGS: Put there the flags used to make your compiler ANSI-compliant.
 #
@@ -78,10 +76,8 @@ ANSIFLAGS := -A
 
 # library linking
 #
-ifndef CLEAN_LIBRARY
-  CLEAN_LIBRARY = $(DELETE) $(PROJECT_LIBRARY)
-endif
-LINK_LIBRARY = $(AR) -r $@ $(OBJECTS_LIST)
+CLEAN_LIBRARY ?= $(DELETE) $(PROJECT_LIBRARY)
+LINK_LIBRARY   = $(AR) -r $@ $(OBJECTS_LIST)
 
 
 # EOF
diff --git a/builds/compiler/visualage.mk b/builds/compiler/visualage.mk
index 21ef12b2..c109659b 100644
--- a/builds/compiler/visualage.mk
+++ b/builds/compiler/visualage.mk
@@ -3,7 +3,7 @@
 #
 
 
-# Copyright 1996-2000, 2003 by
+# Copyright 1996-2000, 2003, 2006 by
 # David Turner, Robert Wilhelm, and Werner Lemberg.
 #
 # This file is part of the FreeType project, and may only be used, modified,
@@ -60,9 +60,7 @@ T := /Fo
 #
 #   These should concern: debug output, optimization & warnings.
 #
-ifndef CFLAGS
-  CFLAGS := /Q- /Gd+ /O2 /G5 /W3 /C
-endif
+CFLAGS ?= /Q- /Gd+ /O2 /G5 /W3 /C
 
 # ANSIFLAGS: Put there the flags used to make your compiler ANSI-compliant.
 #
diff --git a/builds/compiler/visualc.mk b/builds/compiler/visualc.mk
index 594c8199..49c446f5 100644
--- a/builds/compiler/visualc.mk
+++ b/builds/compiler/visualc.mk
@@ -3,7 +3,7 @@
 #
 
 
-# Copyright 1996-2000, 2003, 2005 by
+# Copyright 1996-2000, 2003, 2005, 2006 by
 # David Turner, Robert Wilhelm, and Werner Lemberg.
 #
 # This file is part of the FreeType project, and may only be used, modified,
@@ -66,9 +66,7 @@ TE := /Fe
 #   Use the ANSIFLAGS variable to define the compiler flags used to enfore
 #   ANSI compliance.
 #
-ifndef CFLAGS
-  CFLAGS := /nologo /c /Ox /G5 /W3 /WX
-endif
+CFLAGS ?= /nologo /c /Ox /G5 /W3 /WX
 
 # ANSIFLAGS: Put there the flags used to make your compiler ANSI-compliant.
 #
diff --git a/builds/compiler/watcom.mk b/builds/compiler/watcom.mk
index 12394be4..4db1e7fe 100644
--- a/builds/compiler/watcom.mk
+++ b/builds/compiler/watcom.mk
@@ -3,7 +3,7 @@
 #
 
 
-# Copyright 1996-2000, 2003 by
+# Copyright 1996-2000, 2003, 2006 by
 # David Turner, Robert Wilhelm, and Werner Lemberg.
 #
 # This file is part of the FreeType project, and may only be used, modified,
@@ -63,9 +63,7 @@ T := -FO=
 #   Use the ANSIFLAGS variable to define the compiler flags used to enfore
 #   ANSI compliance.
 #
-ifndef CFLAGS
-  CFLAGS := -zq
-endif
+CFLAGS ?= -zq
 
 # ANSIFLAGS: Put there the flags used to make your compiler ANSI-compliant.
 #
@@ -74,12 +72,10 @@ ANSIFLAGS := -za
 
 # Library linking
 #
-ifndef CLEAN_LIBRARY
-  CLEAN_LIBRARY = $(DELETE) $(subst /,$(SEP),$(PROJECT_LIBRARY))
-endif
-LINK_LIBRARY = $(subst /,$(COMPILER_SEP), \
-                 wlib -q -n $@; \
-                 $(foreach m, $(OBJECTS_LIST), wlib -q $@ +$(m);) \
-                 echo > nul)
+CLEAN_LIBRARY ?= $(DELETE) $(subst /,$(SEP),$(PROJECT_LIBRARY))
+LINK_LIBRARY   = $(subst /,$(COMPILER_SEP), \
+                   wlib -q -n $@; \
+                   $(foreach m, $(OBJECTS_LIST), wlib -q $@ +$(m);) \
+                   echo > nul)
 
 # EOF
diff --git a/builds/compiler/win-lcc.mk b/builds/compiler/win-lcc.mk
index c500d82c..5d02d824 100644
--- a/builds/compiler/win-lcc.mk
+++ b/builds/compiler/win-lcc.mk
@@ -3,7 +3,7 @@
 #
 
 
-# Copyright 1996-2000, 2003 by
+# Copyright 1996-2000, 2003, 2006 by
 # David Turner, Robert Wilhelm, and Werner Lemberg.
 #
 # This file is part of the FreeType project, and may only be used, modified,
@@ -63,9 +63,7 @@ T := -Fo
 #   Use the ANSIFLAGS variable to define the compiler flags used to enfore
 #   ANSI compliance.
 #
-ifndef CFLAGS
-  CFLAGS := -c -g2 -O
-endif
+CFLAGS ?= -c -g2 -O
 
 # ANSIFLAGS: Put there the flags used to make your compiler ANSI-compliant.
 #
diff --git a/builds/detect.mk b/builds/detect.mk
index eeb1300b..6d85f0cd 100644
--- a/builds/detect.mk
+++ b/builds/detect.mk
@@ -38,12 +38,6 @@
 #   TOP_DIR      The top-most directory in the FreeType library source
 #                hierarchy.  If not defined, it will default to `.'.
 
-# If TOP_DIR is not defined, default it to `.'
-#
-ifndef TOP_DIR
-  TOP_DIR := .
-endif
-
 # Set auto-detection default to `ansi' resp. UNIX-like operating systems.
 #
 PLATFORM     := ansi
diff --git a/builds/dos/detect.mk b/builds/dos/detect.mk
index 43c48d0f..cabc6d64 100644
--- a/builds/dos/detect.mk
+++ b/builds/dos/detect.mk
@@ -3,7 +3,7 @@
 #
 
 
-# Copyright 1996-2000, 2003, 2004 by
+# Copyright 1996-2000, 2003, 2004, 2006 by
 # David Turner, Robert Wilhelm, and Werner Lemberg.
 #
 # This file is part of the FreeType project, and may only be used, modified,
@@ -73,9 +73,7 @@ ifeq ($(PLATFORM),dos)
   # Use DJGPP (i.e. gcc) by default.
   #
   CONFIG_FILE := dos-gcc.mk
-  ifndef CC
-    CC        := gcc
-  endif
+  CC          ?= gcc
 
   # additionally, we provide hooks for various other compilers
   #
diff --git a/builds/freetype.mk b/builds/freetype.mk
index 2f9b540c..c60e9eff 100644
--- a/builds/freetype.mk
+++ b/builds/freetype.mk
@@ -105,9 +105,7 @@ CACHE_DIR    := $(PUBLIC_DIR)/cache
 
 # The documentation directory.
 #
-ifndef DOC_DIR
-  DOC_DIR := $(TOP_DIR)/docs/reference
-endif
+DOC_DIR ?= $(TOP_DIR)/docs/reference
 
 # The final name of the library file.
 #
@@ -192,9 +190,7 @@ FREETYPE_H := $(PUBLIC_H) $(BASE_H) $(CONFIG_H) $(CACHE_H) $(DEVEL_H)
 
 # ftsystem component
 #
-ifndef FTSYS_SRC
-  FTSYS_SRC := $(BASE_DIR)/ftsystem.c
-endif
+FTSYS_SRC ?= $(BASE_DIR)/ftsystem.c
 
 FTSYS_OBJ := $(OBJ_DIR)/ftsystem.$O
 
@@ -206,9 +202,7 @@ $(FTSYS_OBJ): $(FTSYS_SRC) $(FREETYPE_H)
 
 # ftdebug component
 #
-ifndef FTDEBUG_SRC
-  FTDEBUG_SRC := $(BASE_DIR)/ftdebug.c
-endif
+FTDEBUG_SRC ?= $(BASE_DIR)/ftdebug.c
 
 FTDEBUG_OBJ := $(OBJ_DIR)/ftdebug.$O
 
diff --git a/builds/os2/os2-dev.mk b/builds/os2/os2-dev.mk
index bd122152..83da8dea 100644
--- a/builds/os2/os2-dev.mk
+++ b/builds/os2/os2-dev.mk
@@ -15,10 +15,6 @@
 # fully.
 
 
-ifndef TOP_DIR
-  TOP_DIR := .
-endif
-
 DEVEL_DIR := $(TOP_DIR)/devel
 
 # include OS/2-specific definitions
diff --git a/builds/toplevel.mk b/builds/toplevel.mk
index 4a6c9fc7..aab0fd11 100644
--- a/builds/toplevel.mk
+++ b/builds/toplevel.mk
@@ -58,9 +58,7 @@ endif
 # FTMODULE_H, as its name suggests, indicates where the FreeType module
 # classes resides.
 #
-ifndef FTMODULE_H
-  FTMODULE_H := $(OBJ_DIR)/ftmodule.h
-endif
+FTMODULE_H ?= $(OBJ_DIR)/ftmodule.h
 
 
 include $(MODULES_CFG)
@@ -74,9 +72,7 @@ MODULES := $(FONT_MODULES)    \
            $(AUX_MODULES)
 
 
-ifndef CONFIG_MK
-  CONFIG_MK := config.mk
-endif
+CONFIG_MK ?= config.mk
 
 # If no configuration sub-makefile is present, or if `setup' is the target
 # to be built, run the auto-detection rules to figure out which
diff --git a/builds/win32/w32-dev.mk b/builds/win32/w32-dev.mk
index bf3fe3ac..00cacb0f 100644
--- a/builds/win32/w32-dev.mk
+++ b/builds/win32/w32-dev.mk
@@ -19,10 +19,6 @@
 #       Shell (_not_ Cygwin BASH)!
 #
 
-ifndef TOP_DIR
-  TOP_DIR := .
-endif
-
 DEVEL_DIR := $(TOP_DIR)/devel
 
 include $(TOP_DIR)/builds/win32/win32-def.mk