diff --git a/Recipe b/Recipe
index 5715938b..33d0f2f7 100644
--- a/Recipe
+++ b/Recipe
@@ -208,9 +208,9 @@ endif
 if HAVE_QUARTZ
 noinst_SCRIPTS = unix/PuTTY.app unix/Pterm.app
 unix/PuTTY.app: unix/putty.bundle puttyapp osxlaunch
-	rm -rf $@ && gtk-mac-bundler $<
+	rm -rf $@ && PUTTY_GTK_PREFIX_FROM_MAKEFILE=$$(pkg-config --variable=prefix gtk+-3.0) gtk-mac-bundler $<
 unix/Pterm.app: unix/pterm.bundle ptermapp osxlaunch
-	rm -rf $@ && gtk-mac-bundler $<
+	rm -rf $@ && PUTTY_GTK_PREFIX_FROM_MAKEFILE=$$(pkg-config --variable=prefix gtk+-3.0) gtk-mac-bundler $<
 endif
 !end
 
diff --git a/unix/pterm.bundle b/unix/pterm.bundle
index 377fee0d..0d701216 100644
--- a/unix/pterm.bundle
+++ b/unix/pterm.bundle
@@ -2,7 +2,11 @@
 <app-bundle>
 
   <meta>
-    <prefix name="default">${env:JHBUILD_PREFIX}</prefix>
+    <!-- If you try to use this script outside the makefile, you'll
+         have to set PUTTY_GTK_PREFIX_FROM_MAKEFILE by hand. See the
+         full rant in putty.bundle for further explanation. -->
+    <prefix name="default">${env:PUTTY_GTK_PREFIX_FROM_MAKEFILE}</prefix>
+
     <run-install-name-tool/>
     <gtk>gtk+-3.0</gtk>
     <!-- Optionally specify a launcher script to use. If the
diff --git a/unix/putty.bundle b/unix/putty.bundle
index 91b0def0..d635c4f2 100644
--- a/unix/putty.bundle
+++ b/unix/putty.bundle
@@ -2,7 +2,41 @@
 <app-bundle>
 
   <meta>
-    <prefix name="default">${env:JHBUILD_PREFIX}</prefix>
+    <!--
+        Set up the pathname prefix where the bundler will look for GTK
+        components such as themes and input method modules.
+
+        This is more of a pain than it ought to be. The example bundle
+        files that come with gtk-mac-bundler set this up by writing
+
+            <prefix name="default">${env:JHBUILD_PREFIX}</prefix>
+
+        which works provided your OS X GTK dev environment was set up
+        by jhbuild. But not everybody's is: some people prefer
+        alternative packaging systems. So that environment variable
+        won't be reliably set in everyone's world.
+
+        The gtk-mac-bundler README suggests that you _ought_ to be
+        able to write this instead:
+
+            <prefix name="default">${pkg:gtk+-3.0:prefix}</prefix>
+
+        which uses pkg-config from $PATH to get the 'prefix' variable.
+        That's surely exactly what you want - except that it doesn't
+        work, because ${pkg:...} is not expanded when processing
+        <prefix> directives in particular!
+
+        So instead, to make this work sensibly whether or not
+        someone's using jhbuild, I work around it by inventing an
+        environment variable of my own and setting that in the
+        Makefile to the value given by the above pkg-config command.
+        It's absurd that I have to, but there we go. As a result, if
+        you try to run the bundler command standalone, you'll find you
+        have to set that variable up manually before you run it.
+
+    -->
+    <prefix name="default">${env:PUTTY_GTK_PREFIX_FROM_MAKEFILE}</prefix>
+
     <run-install-name-tool/>
     <gtk>gtk+-3.0</gtk>
     <!-- Optionally specify a launcher script to use. If the