diff --git a/prebuilt/common/bin/otasigcheck.sh b/prebuilt/common/bin/otasigcheck.sh
index ad7f3a3..99fdaec 100644
--- a/prebuilt/common/bin/otasigcheck.sh
+++ b/prebuilt/common/bin/otasigcheck.sh
@@ -15,14 +15,71 @@
   exit 0
 fi
 
-if [ -f /data/system/packages.xml -a -f /tmp/releasekey ]; then
-  relCert=$(grep -A3 'package name="com.android.htmlviewer"' /data/system/packages.xml  | grep "cert index" | head -n 1 | sed -e 's|.*"\([[:digit:]][[:digit:]]*\)".*|\1|g')
+if [ -f "/data/system/packages.xml" -a -f "/tmp/releasekey" ]; then
+  relkey=$(cat "/tmp/releasekey")
+  OLDIFS="$IFS"
+  IFS=""
+  while read line; do
+    params=${line# *<package *}
+    if [ "$line" != "$params" ]; then
+      kvp=${params%% *}
+      params=${params#* }
+      while [ "$kvp" != "$params" ]; do
+        key=${kvp%%=*}
+        val=${kvp#*=}
+        vlen=$(( ${#val} - 2 ))
+        val=${val:1:$vlen}
+        if [ "$key" = "name" ]; then
+          package="$val"
+        fi
+        kvp=${params%% *}
+        params=${params#* }
+      done
+      continue
+    fi
+    params=${line# *<cert *}
+    if [ "$line" != "$params" ]; then
+      keyidx=""
+      keyval=""
+      kvp=${params%% *}
+      params=${params#* }
+      while [ "$kvp" != "$params" ]; do
+        key=${kvp%%=*}
+        val=${kvp#*=}
+        vlen=$(( ${#val} - 2 ))
+        val=${val:1:$vlen}
+        if [ "$key" = "index" ]; then
+          keyidx="$val"
+        fi
+        if [ "$key" = "key" ]; then
+          keyval="$val"
+        fi
+        kvp=${params%% *}
+        params=${params#* }
+      done
+      if [ -n "$keyidx" ]; then
+        if [ "$package" = "com.android.htmlviewer" ]; then
+          cert_idx="$keyidx"
+        fi
+      fi
+      if [ -n "$keyval" ]; then
+        eval "key_$keyidx=$keyval"
+      fi
+      continue
+    fi
+  done < "/data/system/packages.xml"
+  IFS="$OLDIFS"
 
   # Tools missing? Err on the side of caution and exit cleanly
-  if [ "z$relCert" == "z" ]; then exit 0; fi
+  if [ -z "$cert_idx" ]; then
+    echo "Package cert index not found; skipping signature check..."
+    exit 0
+  fi
 
-  grep "cert index=\"$relCert\"" /data/system/packages.xml | grep -q `cat /tmp/releasekey`
-  if [ $? -ne 0 ]; then
+  varname="key_$cert_idx"
+  eval "pkgkey=\$$varname"
+
+  if [ "$pkgkey" != "$relkey" ]; then
      echo "You have an installed system that isn't signed with this build's key, aborting..."
      exit 124
   fi