diff --git a/build-aux/pre-inst-env.in b/build-aux/pre-inst-env.in
index da9c61c0..3f6201ac 100644
--- a/build-aux/pre-inst-env.in
+++ b/build-aux/pre-inst-env.in
@@ -26,7 +26,7 @@ prefix=${prefix-@prefix@}
 export prefix
 program_prefix=${program_prefix-@program_prefix@}
 
-MES_PREFIX=${MES_PREFIX-${abs_top_srcdir}/mes}
+MES_PREFIX=${MES_PREFIX-${abs_top_srcdir}}
 export MES_PREFIX
 
 GUILE_LOAD_COMPILED_PATH="$abs_top_builddir/scripts:$abs_top_builddir/module${GUILE_LOAD_COMPILED_PATH:+:}$GUILE_LOAD_COMPILED_PATH"
diff --git a/src/mes.c b/src/mes.c
index 81de6a73..d9760fad 100644
--- a/src/mes.c
+++ b/src/mes.c
@@ -1788,6 +1788,7 @@ open_boot ()
   if (getenv ("MES_PREFIX"))
     {
       strcpy (g_datadir, getenv ("MES_PREFIX"));
+      strcpy (g_datadir + strlen (g_datadir), "/mes");
       strcpy (file_name, g_datadir);
       strcpy (file_name + strlen (file_name), "/module/mes/");
       __stdin = try_open_boot (file_name, boot, "MES_PREFIX");
@@ -1809,10 +1810,13 @@ open_boot ()
     }
   if (__stdin < 0)
     {
-      strcpy (g_datadir, "mes");
+      g_datadir[0] = 0;
+      if (getenv ("srcdest"))
+        strcpy (g_datadir, getenv ("srcdest"));
+      strcpy (g_datadir + strlen (g_datadir), "mes");
       strcpy (file_name, g_datadir);
       strcpy (file_name + strlen (file_name), "/module/mes/");
-      __stdin = try_open_boot (file_name, boot, "mes");
+      __stdin = try_open_boot (file_name, boot, "${srcdest}mes");
     }
   if (__stdin < 0)
     {