diff --git a/build-aux/compiler.mak b/build-aux/compiler.mak
index 104e9b3a..b6e9e575 100644
--- a/build-aux/compiler.mak
+++ b/build-aux/compiler.mak
@@ -36,6 +36,9 @@ software_meant_for_sortix:
   endif
 endif
 
+# Determine whether a function is unset or is a Make default.
+is_unset_or_default = $(filter undefined default,$(origin $(1)))
+
 # Provide deprecated CPU variable so makefiles can select CPU-specific dirs.
 ifeq ($(HOST),i486-sortix)
     MACHINE:=i486
@@ -61,66 +64,57 @@ ifndef HOST_TOOL_PREFIX
 endif
 
 # Determine the names of the tools that target the build platform.
-ifndef BUILDCC
-  BUILDCC:=$(BUILD_TOOL_PREFIX)gcc
+ifndef CC_FOR_BUILD
+  CC_FOR_BUILD:=$(BUILD_TOOL_PREFIX)gcc
 endif
-ifndef BUILDCXX
-  BUILDCXX:=$(BUILD_TOOL_PREFIX)g++
+ifndef CXX_FOR_BUILD
+  CXX_FOR_BUILD:=$(BUILD_TOOL_PREFIX)g++
 endif
-ifndef BUILDAR
-  BUILDAR:=$(BUILD_TOOL_PREFIX)ar
+ifndef AR_FOR_BUILD
+  AR_FOR_BUILD:=$(BUILD_TOOL_PREFIX)ar
 endif
-ifndef BUILDAS
-  BUILDAS:=$(BUILD_TOOL_PREFIX)as
+ifndef AS_FOR_BUILD
+  AS_FOR_BUILD:=$(BUILD_TOOL_PREFIX)as
 endif
-ifndef BUILDLD
-  BUILDAS:=$(BUILD_TOOL_PREFIX)ld
+ifndef LD_FOR_BUILD
+  LD_FOR_BUILD:=$(BUILD_TOOL_PREFIX)ld
 endif
-ifndef BUILDOBJCOPY
-  BUILDOBJCOPY:=$(BUILD_TOOL_PREFIX)objcopy
+ifndef OBJCOPY_FOR_BUILD
+  OBJCOPY_FOR_BUILD:=$(BUILD_TOOL_PREFIX)objcopy
 endif
 
 # Determine the names of the tools that target the host platform.
-ifndef HOSTCC
-  HOSTCC:=$(HOST_TOOL_PREFIX)gcc
+ifneq ($(call is_unset_or_default,CC),)
+  CC:=$(HOST_TOOL_PREFIX)gcc
 endif
-ifndef HOSTCXX
-  HOSTCXX:=$(HOST_TOOL_PREFIX)g++
+ifneq ($(call is_unset_or_default,CXX),)
+  CXX:=$(HOST_TOOL_PREFIX)g++
 endif
-ifndef HOSTAR
-  HOSTAR:=$(HOST_TOOL_PREFIX)ar
+ifneq ($(call is_unset_or_default,AR),)
+  AR:=$(HOST_TOOL_PREFIX)ar
 endif
-ifndef HOSTAS
-  HOSTAS:=$(HOST_TOOL_PREFIX)as
+ifneq ($(call is_unset_or_default,AS),)
+  AS:=$(HOST_TOOL_PREFIX)as
 endif
-ifndef HOSTLD
-  HOSTLD:=$(HOST_TOOL_PREFIX)ld
+ifneq ($(call is_unset_or_default,LD),)
+  LD:=$(HOST_TOOL_PREFIX)ld
 endif
-ifndef HOSTOBJCOPY
-  HOSTOBJCOPY:=$(HOST_TOOL_PREFIX)objcopy
+ifneq ($(call is_unset_or_default,OBJCOPY),)
+  OBJCOPY:=$(HOST_TOOL_PREFIX)objcopy
 endif
 ifdef SYSROOT
-  HOSTCC:=$(HOSTCC) --sysroot="$(SYSROOT)"
-  HOSTCXX:=$(HOSTCXX) --sysroot="$(SYSROOT)"
-  HOSTLD:=$(HOSTLD) --sysroot="$(SYSROOT)"
+  CC:=$(CC) --sysroot="$(SYSROOT)"
+  CXX:=$(CXX) --sysroot="$(SYSROOT)"
+  LD:=$(LD) --sysroot="$(SYSROOT)"
 endif
 
-CC:=$(HOSTCC)
-CXX:=$(HOSTCXX)
-AR:=$(HOSTAR)
-AS:=$(HOSTAS)
-LD:=$(HOSTLD)
-OBJCOPY:=$(HOSTOBJCOPY)
-
 # Determine default optimization level.
 DEFAULT_GENERIC_OPTLEVEL_BASE:=-O2 -g
-DEFAULT_BUILD_OPTLEVEL:=$(DEFAULT_GENERIC_OPTLEVEL_BASE)
+DEFAULT_OPTLEVEL_FOR_BUILD:=$(DEFAULT_GENERIC_OPTLEVEL_BASE)
 ifeq ($(BUILD_IS_SORTIX),1)
-  DEFAULT_BUILD_OPTLEVEL+=
+  DEFAULT_OPTLEVEL_FOR_BUILD+=
 endif
-DEFAULT_HOST_OPTLEVEL:=$(DEFAULT_GENERIC_OPTLEVEL_BASE)
 DEFAULT_OPTLEVEL:=$(DEFAULT_GENERIC_OPTLEVEL_BASE)
 ifeq ($(HOST_IS_SORTIX),1)
-  DEFAULT_HOST_OPTLEVEL+=
   DEFAULT_OPTLEVEL+=
 endif
diff --git a/kernel/Makefile b/kernel/Makefile
index 24895ba0..e44adbf7 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -5,7 +5,7 @@ include ../build-aux/version.mak
 include ../build-aux/dirs.mak
 
 # Default values in case the user doesn't override these variables.
-OPTLEVEL?=$(DEFAULT_HOST_OPTLEVEL)
+OPTLEVEL?=$(DEFAULT_OPTLEVEL)
 DISKWRITE?=1
 CPPFLAGS?=
 CXXFLAGS?=$(OPTLEVEL)
@@ -67,8 +67,8 @@ endif
 # Object files that constitute the kernel.
 
 CRTI_OBJ:=$(CPUDIR)/crti.o
-CRTBEGIN_OBJ:=$(shell $(HOSTCXX) $(CXXFLAGS) -print-file-name=crtbegin.o)
-CRTEND_OBJ:=$(shell $(HOSTCXX) $(CXXFLAGS) -print-file-name=crtend.o)
+CRTBEGIN_OBJ:=$(shell $(CXX) $(CXXFLAGS) -print-file-name=crtbegin.o)
+CRTEND_OBJ:=$(shell $(CXX) $(CXXFLAGS) -print-file-name=crtend.o)
 CRTN_OBJ:=$(CPUDIR)/crtn.o
 
 LIBS=\
@@ -176,10 +176,10 @@ headers:
 ifeq ($(CPU),x64)
 
 sortix-x86_64.bin: $(ALLOBJS)
-	$(HOSTCXX) $(CXXFLAGS) -Wl,-Ttext -Wl,100000 -Wl,-z -Wl,max-page-size=0x1000 $(LINK_OBJECTS) -o $@
+	$(CXX) $(CXXFLAGS) -Wl,-Ttext -Wl,100000 -Wl,-z -Wl,max-page-size=0x1000 $(LINK_OBJECTS) -o $@
 
 sortix.bin: sortix-x86_64.bin
-	$(HOSTOBJCOPY) $< -O elf32-i386-sortix $@
+	$(OBJCOPY) $< -O elf32-i386-sortix $@
 
 endif
 
@@ -187,15 +187,15 @@ endif
 ifeq ($(CPU),x86)
 
 sortix.bin: $(ALLOBJS)
-	$(HOSTCXX) $(CXXFLAGS) -Wl,-Ttext -Wl,100000 $(LINK_OBJECTS) -o $@
+	$(CXX) $(CXXFLAGS) -Wl,-Ttext -Wl,100000 $(LINK_OBJECTS) -o $@
 
 endif
 
 %.o: %.cpp
-	$(HOSTCXX) -c $< -o $@ $(CPPFLAGS) $(CXXFLAGS)
+	$(CXX) -c $< -o $@ $(CPPFLAGS) $(CXXFLAGS)
 
 %.o: %.S
-	$(HOSTCXX) -c $< -o $@ $(CPPFLAGS) $(CXXFLAGS)
+	$(CXX) -c $< -o $@ $(CPPFLAGS) $(CXXFLAGS)
 
 clean:
 	rm -f $(ALLOBJS) sortix.bin
diff --git a/libc/Makefile b/libc/Makefile
index 9b76436a..a491c1fd 100644
--- a/libc/Makefile
+++ b/libc/Makefile
@@ -4,7 +4,7 @@ include ../build-aux/compiler.mak
 include ../build-aux/version.mak
 include ../build-aux/dirs.mak
 
-OPTLEVEL?=$(DEFAULT_HOST_OPTLEVEL)
+OPTLEVEL?=$(DEFAULT_OPTLEVEL)
 
 CPUDIR:=$(CPU)
 
@@ -684,19 +684,19 @@ libs-kernel: $(BINSKERNEL)
 FORCE:
 
 libc.a: $(OBJS)
-	$(HOSTAR) rcs $@ $(OBJS)
+	$(AR) rcs $@ $(OBJS)
 
 libdl.a:
-	$(HOSTAR) rcs $@
+	$(AR) rcs $@
 
 libg.a:
-	$(HOSTAR) rcs $@
+	$(AR) rcs $@
 
 libk.a: $(LIBK_OBJS)
-	$(HOSTAR) rcs $@ $(LIBK_OBJS)
+	$(AR) rcs $@ $(LIBK_OBJS)
 
 librt.a:
-	$(HOSTAR) rcs $@
+	$(AR) rcs $@
 
 crt0.o: $(CPUDIR)/crt0.o
 	ln -f $< $@
@@ -717,23 +717,23 @@ headers:
 
 # standard library
 %.o: %.c
-	$(HOSTCC) -c $< -o $@ $(CPPFLAGS) $(FLAGS) $(CFLAGS)
+	$(CC) -c $< -o $@ $(CPPFLAGS) $(FLAGS) $(CFLAGS)
 
 %.o: %.cpp
-	$(HOSTCXX) -c $< -o $@ $(CPPFLAGS) $(FLAGS) $(CXXFLAGS)
+	$(CXX) -c $< -o $@ $(CPPFLAGS) $(FLAGS) $(CXXFLAGS)
 
 %.o: %.S
-	$(HOSTCXX) -c $< -o $@ $(CPPFLAGS) $(FLAGS) $(CFLAGS)
+	$(CXX) -c $< -o $@ $(CPPFLAGS) $(FLAGS) $(CFLAGS)
 
 # libk
 %.libk.o: %.c
-	$(HOSTCC) -c $< -o $@ $(LIBK_CPPFLAGS) $(LIBK_FLAGS) $(LIBK_CFLAGS)
+	$(CC) -c $< -o $@ $(LIBK_CPPFLAGS) $(LIBK_FLAGS) $(LIBK_CFLAGS)
 
 %.libk.o: %.cpp
-	$(HOSTCXX) -c $< -o $@ $(LIBK_CPPFLAGS) $(LIBK_FLAGS) $(LIBK_CXXFLAGS)
+	$(CXX) -c $< -o $@ $(LIBK_CPPFLAGS) $(LIBK_FLAGS) $(LIBK_CXXFLAGS)
 
 %.libk.o: %.S
-	$(HOSTCC) -c $< -o $@ $(LIBK_CPPFLAGS) $(LIBK_FLAGS) $(LIBK_CFLAGS)
+	$(CC) -c $< -o $@ $(LIBK_CPPFLAGS) $(LIBK_FLAGS) $(LIBK_CFLAGS)
 
 clean:
 	rm -f *.o */*.o */*/*.o *.a
diff --git a/libm/Makefile b/libm/Makefile
index 3f84f4a3..275030d2 100644
--- a/libm/Makefile
+++ b/libm/Makefile
@@ -3,7 +3,7 @@ include ../build-aux/compiler.mak
 include ../build-aux/version.mak
 include ../build-aux/dirs.mak
 
-OPTLEVEL?=$(DEFAULT_HOST_OPTLEVEL)
+OPTLEVEL?=$(DEFAULT_OPTLEVEL)
 CFLAGS?=$(OPTLEVEL)
 
 # TODO: Better detection of the proper subdirectory here!
@@ -383,13 +383,13 @@ arch/i387/s_modf.o: src/s_modf.c
 headers:
 
 libm.a: $(OBJS)
-	$(HOSTAR) rcs $@ $(OBJS)
+	$(AR) rcs $@ $(OBJS)
 
 %.o: %.S
-	$(HOSTCC) -c $< -o $@ $(CPPFLAGS) $(CFLAGS)
+	$(CC) -c $< -o $@ $(CPPFLAGS) $(CFLAGS)
 
 %.o: %.c
-	$(HOSTCC) -c $< -o $@ $(CPPFLAGS) $(CFLAGS)
+	$(CC) -c $< -o $@ $(CPPFLAGS) $(CFLAGS)
 
 clean:
 	rm -f $(BINS) $(OBJS) $(ARCH_SUBDIR)/*.o src/*.o */*.o arch/*/*.o
diff --git a/libpthread/Makefile b/libpthread/Makefile
index 96e72c60..b48b0038 100644
--- a/libpthread/Makefile
+++ b/libpthread/Makefile
@@ -4,7 +4,7 @@ include ../build-aux/compiler.mak
 include ../build-aux/version.mak
 include ../build-aux/dirs.mak
 
-OPTLEVEL?=$(DEFAULT_HOST_OPTLEVEL)
+OPTLEVEL?=$(DEFAULT_OPTLEVEL)
 CXXFLAGS?=$(OPTLEVEL)
 CPPFLAGS?=
 
@@ -77,10 +77,10 @@ headers:
 libs: $(BINS)
 
 libpthread.a: $(OBJS)
-	$(HOSTAR) rcs $@ $(OBJS)
+	$(AR) rcs $@ $(OBJS)
 
 %.o: %.c++
-	$(HOSTCXX) -std=gnu++11 -c $< -o $@ $(CPPFLAGS) $(CXXFLAGS)
+	$(CXX) -std=gnu++11 -c $< -o $@ $(CPPFLAGS) $(CXXFLAGS)
 
 clean:
 	rm -f $(BINS) $(OBJS) *.o