diff --git a/pisi/operations/build.py b/pisi/operations/build.py
index 25961464..7025d0a1 100644
--- a/pisi/operations/build.py
+++ b/pisi/operations/build.py
@@ -694,6 +694,10 @@ class Builder:
         # find previous build in packages dir
         found = []
         def locate_old_package(old_package_fn):
+            if not old_package_fn.endswith(ctx.const.package_suffix) or \
+                    old_package_fn.endswith(ctx.const.delta_package_suffix):
+                return
+
             if pisi.util.is_package_name(os.path.basename(old_package_fn), package_name):
                 try:
                     old_pkg = pisi.package.Package(old_package_fn, 'r')