diff --git a/src/docx/opc/phys_pkg.py b/src/docx/opc/phys_pkg.py
index 5ec32237c..0a379f3f3 100644
--- a/src/docx/opc/phys_pkg.py
+++ b/src/docx/opc/phys_pkg.py
@@ -15,10 +15,14 @@ def __new__(cls, pkg_file):
         if isinstance(pkg_file, str):
             if os.path.isdir(pkg_file):
                 reader_cls = _DirPkgReader
+            elif not os.path.isfile(pkg_file):
+                raise FileNotFoundError("No such file or directory: '%s'" % pkg_file)
             elif is_zipfile(pkg_file):
                 reader_cls = _ZipPkgReader
             else:
-                raise PackageNotFoundError("Package not found at '%s'" % pkg_file)
+                raise PackageNotFoundError(
+                    "Package at '%s' is not a ZIP archive" % pkg_file
+                )
         else:  # assume it's a stream and pass it to Zip reader to sort out
             reader_cls = _ZipPkgReader
 
diff --git a/tests/opc/test_phys_pkg.py b/tests/opc/test_phys_pkg.py
index 6de0d868b..239992cea 100644
--- a/tests/opc/test_phys_pkg.py
+++ b/tests/opc/test_phys_pkg.py
@@ -64,10 +64,17 @@ def dir_reader(self):
 
 
 class DescribePhysPkgReader:
-    def it_raises_when_pkg_path_is_not_a_package(self):
-        with pytest.raises(PackageNotFoundError):
+    def it_raises_when_pkg_path_does_not_exist(self):
+        with pytest.raises(FileNotFoundError):
             PhysPkgReader("foobar")
 
+    def it_raises_when_pkg_path_exists_but_is_not_a_zip(self, tmpdir):
+        not_a_pkg = str(tmpdir.join("not-a-package.docx"))
+        with open(not_a_pkg, "w") as f:
+            f.write("not a zip")
+        with pytest.raises(PackageNotFoundError):
+            PhysPkgReader(not_a_pkg)
+
 
 class DescribeZipPkgReader:
     def it_is_used_by_PhysPkgReader_when_pkg_is_a_zip(self):