diff --git a/.INSTALL.in b/.INSTALL.in
index 5ee0dc94e..26195acb6 100755
--- a/.INSTALL.in
+++ b/.INSTALL.in
@@ -95,6 +95,21 @@
 # and read the Mercury documentation in the `doc' directory while you are
 # waiting.
 
+if pwd | grep ' '
+then
+    echo "The name of the current directory contains spaces."
+    echo "Mercury cannot be installed from such directories."
+    exit 1
+fi
+
+if test ! -d boehm_gc
+then
+    echo "This directory does not contain a complete source distribution."
+    echo "If you are trying to compile a workspace checked out of git,"
+    echo "you will need to read and follow INSTALL.git, not INSTALL."
+    exit 1
+fi
+
 sh configure &&
 make &&
 make install
diff --git a/INSTALL.git b/INSTALL.git
index fce20aceb..f2ee0b143 100755
--- a/INSTALL.git
+++ b/INSTALL.git
@@ -40,6 +40,13 @@
 #	   If you don't want to do a parallel make, comment out the
 #	   `parallel=-j3' line below.
 
+if pwd | grep ' '
+then
+    echo "The name of the current directory contains spaces."
+    echo "Mercury cannot be installed from such directories."
+    exit 1
+fi
+
 parallel=-j3
 
 ./prepare.sh &&
diff --git a/Mmakefile b/Mmakefile
index 30ce87e43..a7d95ae90 100644
--- a/Mmakefile
+++ b/Mmakefile
@@ -417,6 +417,7 @@ README: .README.in VERSION
 
 INSTALL: .INSTALL.in VERSION
 	sed 's/@VERSION@/$(VERSION)/g' .INSTALL.in > INSTALL
+	chmod a+x INSTALL
 
 ifeq ("$(LYNX)","")
 HTML_TO_TEXT = cat