diff --git a/crup-runner.sh b/crup-runner.sh
index 9b17413dc..97e79ce45 100755
--- a/crup-runner.sh
+++ b/crup-runner.sh
@@ -9,13 +9,39 @@ solution="${1%%/*}"
 cd "$solution"
 if [ "$solution" = "$1" ]; then
   shift
-  $@ | sed "s/^/[$solution] /g" 1>&2
+  # Don't "pull" if checkout is not on a named branch
+  if test "$2" = "pull" && ( ! git symbolic-ref HEAD >/dev/null 2>/dev/null ); then
+    first_args="$1 fetch"
+  else
+    first_args="$1 $2"
+  fi
+  shift 2
+  $first_args $@ | sed "s/^/[$solution] /g" 1>&2
   if [ $? -ne 0 ]; then
     exit $?
   fi
   "$GIT_EXE" submodule --quiet sync
   "$GIT_EXE" ls-files -s | grep ^160000 | awk '{print $4}' |
-  sed "s/^/$solution\//g"
+  while read submod; do
+    # Check whether this submodule should be ignored or updated.
+    # If it's a new submodule, match the os specified in .gitmodules against
+    # the os specified in .git/config.
+    update_policy=$(git config "submodule.$submod.update" 2>/dev/null)
+    if [ -z "$update_policy" ]; then
+      target_os=$(git config target.os 2>/dev/null)
+      submod_os=$(git config -f .gitmodules "submodule.$submod.os" 2>/dev/null)
+      if [ -n "$target_os" -a -n "$submod_os" ] &&
+          [ "$submod_os" != "all" -a "$submod_os" != "$target_os" ]; then
+        update_policy=none
+      else
+        update_policy=checkout
+      fi
+      git config "submodule.$submod.update" $update_policy 2>/dev/null
+    fi
+    if [ "$update_policy" != "none" ]; then
+      echo "$solution/$submod"
+    fi
+  done
   status=$?
 else
   submodule="${1#*/}"
diff --git a/git-crup b/git-crup
index fd81c893d..8633aa20d 100755
--- a/git-crup
+++ b/git-crup
@@ -53,7 +53,7 @@ serial_update() {
     $GIT_EXE submodule --quiet sync
     $GIT_EXE ls-files -s | grep ^160000 | awk '{print $4}' |
     while read submod; do
-      $GIT_EXE submodule update --init "$submod" | sed "s|^|[$1/$submod] |g"
+      "$crup_runner" "$1/$submod"
     done
   )
 }
@@ -119,7 +119,6 @@ else
 fi
 
 set -o pipefail
-
 if test "$xargs_parallel" = "yes"; then
   ( ls -d */.git | sed 's/\/\.git$//' |
    xargs $max_lines $replace_arg -P "$j" \