diff --git a/contrib/asdf-module.mk b/contrib/asdf-module.mk
index 97b1f341b..498f71428 100644
--- a/contrib/asdf-module.mk
+++ b/contrib/asdf-module.mk
@@ -6,7 +6,7 @@
 # ones as dependencies.
 
 UNAME:=$(shell uname -s)
-DEST=$(SBCL_PWD)/obj/sbcl-home/contrib/
+DEST=$(SBCL_TOP)/obj/sbcl-home/contrib/
 FASL=$(DEST)/$(SYSTEM).fasl
 ASD=$(DEST)/$(SYSTEM).asd
 
diff --git a/contrib/asdf-stub.lisp b/contrib/asdf-stub.lisp
index 754eeb1b4..c6da6cc6f 100644
--- a/contrib/asdf-stub.lisp
+++ b/contrib/asdf-stub.lisp
@@ -14,9 +14,9 @@ sb-ext::(declaim (unmuffle-conditions sb-kernel:redefinition-warning))
 
 (defun setup-asdf-contrib ()
   ;;(setf *resolve-symlinks* nil)
-  (let* ((sbcl-pwd (getenv-pathname "SBCL_PWD" :ensure-directory t))
-         (src-contrib (subpathname sbcl-pwd "contrib/"))
-         (asdf-cache (subpathname sbcl-pwd "obj/asdf-cache/"))
+  (let* ((sbcl-top (merge-pathnames (getenv-pathname "SBCL_TOP" :ensure-directory t)))
+         (src-contrib (subpathname sbcl-top "contrib/"))
+         (asdf-cache (subpathname sbcl-top "obj/asdf-cache/"))
          (source-registry '(:source-registry :ignore-inherited-configuration))
          (output-translations `(:output-translations (,(namestring src-contrib)
                                                       ,(namestring asdf-cache))
@@ -49,9 +49,9 @@ sb-ext::(declaim (unmuffle-conditions sb-kernel:redefinition-warning))
         (append '(:sb-building-contrib) sb-impl:+internal-features+ *features*))
   (setup-asdf-contrib)
   (let* ((name (string-downcase system))
-         (sbcl-pwd (getenv-pathname "SBCL_PWD" :ensure-directory t))
-         (out-contrib (subpathname sbcl-pwd "obj/sbcl-home/contrib/"))
-         (cache-module (subpathname sbcl-pwd (format nil "obj/asdf-cache/~a/" name)))
+         (sbcl-top (merge-pathnames (getenv-pathname "SBCL_TOP" :ensure-directory t)))
+         (out-contrib (subpathname sbcl-top "obj/sbcl-home/contrib/"))
+         (cache-module (subpathname sbcl-top (format nil "obj/asdf-cache/~a/" name)))
          (system (find-system name))
          (system.fasl (output-file 'compile-bundle-op system))
          (module.fasl (subpathname out-contrib (strcat name ".fasl")))
diff --git a/contrib/asdf/Makefile b/contrib/asdf/Makefile
index 1fd4a3b1b..a641122cd 100644
--- a/contrib/asdf/Makefile
+++ b/contrib/asdf/Makefile
@@ -1,4 +1,4 @@
-DEST=$(SBCL_PWD)/obj/sbcl-home/contrib/
+DEST=$(SBCL_TOP)/obj/sbcl-home/contrib/
 ASDF_FASL=$(DEST)/asdf.fasl
 UIOP_FASL=$(DEST)/uiop.fasl
 FASL=$(UIOP_FASL) $(ASDF_FASL)
@@ -7,12 +7,12 @@ FROB_READTABLE='(setf (sb-ext:readtable-base-char-preference *readtable*) :both)
 fasl:: $(UIOP_FASL) $(ASDF_FASL)
 $(UIOP_FASL):: uiop.lisp ../../output/sbcl.core
 	mkdir -p $(DEST)
-	$(SBCL) --eval $(FROB_READTABLE) --eval '(compile-file #p"SYS:CONTRIB;ASDF;UIOP.LISP" :print nil :output-file (parse-native-namestring "$@"))' </dev/null
+	$(SBCL) --eval $(FROB_READTABLE) --eval '(compile-file #p"SYS:CONTRIB;ASDF;UIOP.LISP" :print nil :output-file (merge-pathnames (parse-native-namestring "$@")))' </dev/null
 
 $(ASDF_FASL):: asdf.lisp ../../output/sbcl.core $(UIOP_FASL)
 	if [ -d asdf-upstream ] ; then rm -rf asdf-upstream ; fi
 	mkdir -p $(DEST)
-	$(SBCL) --eval $(FROB_READTABLE) --eval '(compile-file #p"SYS:CONTRIB;ASDF;ASDF.LISP" :print nil :output-file (parse-native-namestring "$@"))' </dev/null
+	$(SBCL) --eval $(FROB_READTABLE) --eval '(compile-file #p"SYS:CONTRIB;ASDF;ASDF.LISP" :print nil :output-file (merge-pathnames (parse-native-namestring "$@")))' </dev/null
 
 install::
 	cp $(FASL) "$(BUILD_ROOT)$(INSTALL_DIR)"
diff --git a/install.sh b/install.sh
index 22e04b770..1246ecf59 100755
--- a/install.sh
+++ b/install.sh
@@ -120,12 +120,12 @@ done
 
 # installing contrib
 
-. ./sbcl-pwd.sh
-sbcl_pwd
+# See make-target-contrib.sh for this variable.
+SBCL_TOP="../../"
 
-SBCL="$SBCL_PWD/src/runtime/sbcl --noinform --core $SBCL_PWD/output/sbcl.core --no-userinit --no-sysinit --disable-debugger"
+SBCL="$SBCL_TOP/src/runtime/sbcl --noinform --core $SBCL_TOP/output/sbcl.core --no-userinit --no-sysinit --disable-debugger"
 SBCL_BUILDING_CONTRIB=1
-export SBCL SBCL_BUILDING_CONTRIB SBCL_PWD
+export SBCL SBCL_BUILDING_CONTRIB SBCL_TOP
 
 . ./find-gnumake.sh
 find_gnumake
diff --git a/make-target-contrib.sh b/make-target-contrib.sh
index 217b5b2e0..4a29e312d 100755
--- a/make-target-contrib.sh
+++ b/make-target-contrib.sh
@@ -35,16 +35,17 @@ export CC LANG LC_ALL
 # Load our build configuration
 . output/build-config
 
-. ./sbcl-pwd.sh
-sbcl_pwd
+## All programs spawned by make-target-contrib.sh that use this
+## variable or anything derived from it are started with CWD
+## contrib/<contrib_name>/. Keeping this a relative pathname to the
+## toplevel source directory makes the shell and make portions of the
+## build system robust against funny stuff in PWD.
+SBCL_TOP="../../"
 
-SBCL_HOME="$SBCL_PWD/obj/sbcl-home"
-export SBCL_HOME SBCL_PWD
-if [ "$OSTYPE" = "cygwin" ] ; then
-    SBCL_PWD=`echo $SBCL_PWD | sed s/\ /\\\\\\\\\ /g`
-fi
+SBCL_HOME="$SBCL_TOP/obj/sbcl-home"
+export SBCL_HOME SBCL_TOP
 
-SBCL="$SBCL_PWD/src/runtime/sbcl --noinform --core $SBCL_PWD/output/sbcl.core \
+SBCL="$SBCL_TOP/src/runtime/sbcl --noinform --core $SBCL_TOP/output/sbcl.core \
 --lose-on-corruption --disable-debugger --no-sysinit --no-userinit"
 SBCL_BUILDING_CONTRIB=1
 export SBCL SBCL_BUILDING_CONTRIB