diff --git a/upload.sh b/upload.sh
index 9161db3..10229e2 100644
--- a/upload.sh
+++ b/upload.sh
@@ -38,12 +38,11 @@ if [ ! -z "$UPLOADTOOL_SUFFIX" ] ; then
   else
     RELEASE_NAME="continuous-$UPLOADTOOL_SUFFIX"
     RELEASE_TITLE="Continuous build ($UPLOADTOOL_SUFFIX)"
-    if [ ! -z "$UPLOADTOOL_ISPRERELEASE" ] ; then
-      is_prerelease="false"
-    else
-      is_prerelease="$UPLOADTOOL_ISPRERELEASE"
-    fi
-
+    if [ "$UPLOADTOOL_ISPRERELEASE" = "true" ] ; then
+	  is_prerelease="true"
+	else
+	  is_prerelease="false"
+	fi
   fi
 else
   # ,, is a bash-ism to convert variable to lower case
@@ -52,11 +51,11 @@ else
       # Do not use "latest" as it is reserved by GitHub
       RELEASE_NAME="continuous"
       RELEASE_TITLE="Continuous build"
-      if [ ! -z "$UPLOADTOOL_ISPRERELEASE" ] ; then
-        is_prerelease="false"
-      else
-        is_prerelease="$UPLOADTOOL_ISPRERELEASE"
-      fi
+      if [ "$UPLOADTOOL_ISPRERELEASE" = "true" ] ; then
+	    is_prerelease="true"
+	  else
+	    is_prerelease="false"
+	  fi
       ;;
     *-alpha*|*-beta*|*-rc*)
       RELEASE_NAME="$TRAVIS_TAG"