diff --git a/ChangeLog b/ChangeLog
index 5b63b77..36098f9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2021-01-10  Werner Lemberg  <wl@gnu.org>
+
+	* builds/*: s/BUILD_DIR/PLATFORM_DIR/.
+
+	The old variable name caused confusion.
+
 2021-01-08  Alexei Podtelezhnikov  <apodtele@gmail.com>
 
 	[builds] Revert `FTMODULE_H' changes.
diff --git a/builds/ansi/ansi-def.mk b/builds/ansi/ansi-def.mk
index f8d4ab6..35663d1 100644
--- a/builds/ansi/ansi-def.mk
+++ b/builds/ansi/ansi-def.mk
@@ -13,11 +13,11 @@
 # fully.
 
 
-DELETE    := rm -f
-CAT       := cat
-SEP       := /
-BUILD_DIR := $(TOP_DIR)/builds/ansi
-PLATFORM  := ansi
+DELETE       := rm -f
+CAT          := cat
+SEP          := /
+PLATFORM_DIR := $(TOP_DIR)/builds/ansi
+PLATFORM     := ansi
 
 # This is used for `make refdoc' and `make refdoc-venv'
 #
diff --git a/builds/beos/beos-def.mk b/builds/beos/beos-def.mk
index 07b7711..6e5db16 100644
--- a/builds/beos/beos-def.mk
+++ b/builds/beos/beos-def.mk
@@ -15,11 +15,11 @@
 # fully.
 
 
-DELETE    := rm -f
-CAT       := cat
-SEP       := /
-BUILD_DIR := $(TOP_DIR)/builds/beos
-PLATFORM  := beos
+DELETE       := rm -f
+CAT          := cat
+SEP          := /
+PLATFORM_DIR := $(TOP_DIR)/builds/beos
+PLATFORM     := beos
 
 # This is used for `make refdoc' and `make refdoc-venv'
 #
diff --git a/builds/beos/detect.mk b/builds/beos/detect.mk
index 5b92512..30238d3 100644
--- a/builds/beos/detect.mk
+++ b/builds/beos/detect.mk
@@ -27,11 +27,11 @@
 
 ifeq ($(PLATFORM),beos)
 
-  DELETE      := rm -f
-  CAT         := cat
-  SEP         := /
-  BUILD_DIR   := $(TOP_DIR)/builds/beos
-  CONFIG_FILE := beos.mk
+  DELETE         := rm -f
+  CAT            := cat
+  SEP            := /
+  PLATFORM_DIR   := $(TOP_DIR)/builds/beos
+  CONFIG_FILE    := beos.mk
 
   setup: std_setup
 
diff --git a/builds/detect.mk b/builds/detect.mk
index 94627fc..55563d7 100644
--- a/builds/detect.mk
+++ b/builds/detect.mk
@@ -16,7 +16,7 @@
 # This sub-Makefile is in charge of detecting the current platform.  It sets
 # the following variables:
 #
-#   BUILD_DIR    The configuration and system-specific directory.  Usually
+#   PLATFORM_DIR The configuration and system-specific directory.  Usually
 #                `builds/$(PLATFORM)' but can be different for custom builds
 #                of the library.
 #
@@ -49,8 +49,8 @@
 BUILD_CONFIG := $(TOP_DIR)/builds
 
 # These two assignments must be delayed.
-BUILD_DIR    = $(BUILD_CONFIG)/$(PLATFORM)
-CONFIG_RULES = $(BUILD_DIR)/$(CONFIG_FILE)
+PLATFORM_DIR = $(BUILD_CONFIG)/$(PLATFORM)
+CONFIG_RULES = $(PLATFORM_DIR)/$(CONFIG_FILE)
 
 # We define the BACKSLASH variable to hold a single back-slash character.
 # This is needed because a line like
@@ -113,7 +113,7 @@
 	$(info )
 	$(info $(empty)  platform                    $(PLATFORM))
 	$(info $(empty)  compiler                    $(CC))
-	$(info $(empty)  configuration directory     $(subst /,$(SEP),$(BUILD_DIR)))
+	$(info $(empty)  configuration directory     $(subst /,$(SEP),$(PLATFORM_DIR)))
 	$(info $(empty)  configuration rules         $(subst /,$(SEP),$(CONFIG_RULES)))
 	$(info )
 	$(info If this does not correspond to your system or settings please remove the file)
diff --git a/builds/dos/dos-def.mk b/builds/dos/dos-def.mk
index 067d1d4..5ef9c30 100644
--- a/builds/dos/dos-def.mk
+++ b/builds/dos/dos-def.mk
@@ -13,11 +13,11 @@
 # fully.
 
 
-DELETE    := del
-CAT       := type
-SEP       := $(strip \ )
-BUILD_DIR := $(TOP_DIR)/builds/dos
-PLATFORM  := dos
+DELETE       := del
+CAT          := type
+SEP          := $(strip \ )
+PLATFORM_DIR := $(TOP_DIR)/builds/dos
+PLATFORM     := dos
 
 # This is used for `make refdoc' and `make refdoc-venv'
 #
diff --git a/builds/freetype.mk b/builds/freetype.mk
index 71d3a48..78f5b16 100644
--- a/builds/freetype.mk
+++ b/builds/freetype.mk
@@ -20,8 +20,8 @@
 # The following variables (set by other Makefile components, in the
 # environment, or on the command line) are used:
 #
-#   BUILD_DIR      The architecture dependent directory,
-#                  e.g. `$(TOP_DIR)/builds/unix'.  Added to INCLUDES also.
+#   PLATFORM_DIR   The architecture-dependent directory,
+#                  e.g., `$(TOP_DIR)/builds/unix'.  Added to INCLUDES also.
 #
 #   OBJ_DIR        The directory in which object files are created.
 #
@@ -121,7 +121,7 @@
 #
 INCLUDES := $(subst /,$(COMPILER_SEP),$(OBJ_DIR) \
                                       $(DEVEL_DIR) \
-                                      $(BUILD_DIR) \
+                                      $(PLATFORM_DIR) \
                                       $(TOP_DIR)/include)
 
 INCLUDE_FLAGS := $(INCLUDES:%=$I%)
@@ -175,16 +175,16 @@
 # changes, the whole library is recompiled.
 #
 ifneq ($(wildcard $(OBJ_DIR)/ftoption.h),)
-  FTOPTION_H    := $(OBJ_DIR)/ftoption.h
-else ifneq ($(wildcard $(BUILD_DIR)/ftoption.h),)
-  FTOPTION_H    := $(BUILD_DIR)/ftoption.h
+  FTOPTION_H := $(OBJ_DIR)/ftoption.h
+else ifneq ($(wildcard $(PLATFORM_DIR)/ftoption.h),)
+  FTOPTION_H := $(PLATFORM_DIR)/ftoption.h
 endif
 
 PUBLIC_H   := $(wildcard $(PUBLIC_DIR)/*.h)
 INTERNAL_H := $(wildcard $(INTERNAL_DIR)/*.h) \
               $(wildcard $(SERVICES_DIR)/*.h)
 CONFIG_H   := $(wildcard $(CONFIG_DIR)/*.h) \
-              $(wildcard $(BUILD_DIR)/config/*.h) \
+              $(wildcard $(PLATFORM_DIR)/config/*.h) \
               $(FTMODULE_H) \
               $(FTOPTION_H)
 DEVEL_H    := $(wildcard $(TOP_DIR)/devel/*.h)
diff --git a/builds/os2/os2-def.mk b/builds/os2/os2-def.mk
index b097654..e0d1e3d 100644
--- a/builds/os2/os2-def.mk
+++ b/builds/os2/os2-def.mk
@@ -13,11 +13,11 @@
 # fully.
 
 
-DELETE    := del
-CAT       := type
-SEP       := $(strip \ )
-BUILD_DIR := $(TOP_DIR)/builds/os2
-PLATFORM  := os2
+DELETE       := del
+CAT          := type
+SEP          := $(strip \ )
+PLATFORM_DIR := $(TOP_DIR)/builds/os2
+PLATFORM     := os2
 
 # This is used for `make refdoc' and `make refdoc-venv'
 #
diff --git a/builds/unix/configure.raw b/builds/unix/configure.raw
index 56b0bce..876ba90 100644
--- a/builds/unix/configure.raw
+++ b/builds/unix/configure.raw
@@ -204,7 +204,7 @@
    -o "$ac_cv_func_mmap_fixed_mapped" != "yes"; then
   FTSYS_SRC='$(BASE_DIR)/ftsystem.c'
 else
-  FTSYS_SRC='$(BUILD_DIR)/ftsystem.c'
+  FTSYS_SRC='$(PLATFORM_DIR)/ftsystem.c'
 
   AC_CHECK_DECLS([munmap],
     [],
diff --git a/builds/unix/install.mk b/builds/unix/install.mk
index aa25187..7a58802 100644
--- a/builds/unix/install.mk
+++ b/builds/unix/install.mk
@@ -62,7 +62,7 @@
           $(DESTDIR)$(includedir)/freetype2/freetype/config/ftmodule.h
 	$(INSTALL_DATA) $(OBJ_BUILD)/ftoption.h                        \
           $(DESTDIR)$(includedir)/freetype2/freetype/config/ftoption.h
-	$(INSTALL_SCRIPT) -m 644 $(BUILD_DIR)/freetype2.m4             \
+	$(INSTALL_SCRIPT) -m 644 $(PLATFORM_DIR)/freetype2.m4          \
           $(DESTDIR)$(datadir)/aclocal/freetype2.m4
 	$(INSTALL_SCRIPT) -m 644 $(OBJ_BUILD)/freetype2.pc             \
           $(DESTDIR)$(libdir)/pkgconfig/freetype2.pc
diff --git a/builds/unix/unix-cc.in b/builds/unix/unix-cc.in
index 9dabb24..7d20414 100644
--- a/builds/unix/unix-cc.in
+++ b/builds/unix/unix-cc.in
@@ -14,7 +14,7 @@
 
 CC           := @CC@
 COMPILER_SEP := $(SEP)
-FT_LIBTOOL_DIR ?= $(BUILD_DIR)
+FT_LIBTOOL_DIR ?= $(PLATFORM_DIR)
 
 LIBTOOL := $(FT_LIBTOOL_DIR)/libtool
 
diff --git a/builds/unix/unix-def.in b/builds/unix/unix-def.in
index 5e04f1c..5f91237 100644
--- a/builds/unix/unix-def.in
+++ b/builds/unix/unix-def.in
@@ -27,7 +27,7 @@
 BIN    := bin
 
 # this is used for `make distclean' and `make install'
-OBJ_BUILD ?= $(BUILD_DIR)
+OBJ_BUILD ?= $(PLATFORM_DIR)
 
 # don't use `:=' here since the path stuff will be included after this file
 #
diff --git a/builds/unix/unix.mk b/builds/unix/unix.mk
index e08727d..ddc4abd 100644
--- a/builds/unix/unix.mk
+++ b/builds/unix/unix.mk
@@ -13,8 +13,8 @@
 # fully.
 
 # We need these declarations here since unix-def.mk is a generated file.
-BUILD_DIR := $(TOP_DIR)/builds/unix
-PLATFORM  := unix
+PLATFORM_DIR := $(TOP_DIR)/builds/unix
+PLATFORM     := unix
 
 have_mk := $(wildcard $(OBJ_DIR)/unix-def.mk)
 ifneq ($(have_mk),)
@@ -22,8 +22,8 @@
   include $(OBJ_DIR)/unix-def.mk
   include $(OBJ_DIR)/unix-cc.mk
 else
-  include $(BUILD_DIR)/unix-def.mk
-  include $(BUILD_DIR)/unix-cc.mk
+  include $(PLATFORM_DIR)/unix-def.mk
+  include $(PLATFORM_DIR)/unix-cc.mk
 endif
 
 ifdef BUILD_PROJECT
diff --git a/builds/windows/win32-def.mk b/builds/windows/win32-def.mk
index f759853..f6689c5 100644
--- a/builds/windows/win32-def.mk
+++ b/builds/windows/win32-def.mk
@@ -13,11 +13,11 @@
 # fully.
 
 
-DELETE    := del
-CAT       := type
-SEP       := $(strip \ )
-BUILD_DIR := $(TOP_DIR)/builds/windows
-PLATFORM  := windows
+DELETE       := del
+CAT          := type
+SEP          := $(strip \ )
+PLATFORM_DIR := $(TOP_DIR)/builds/windows
+PLATFORM     := windows
 
 # This is used for `make refdoc' and `make refdoc-venv'
 #