diff --git a/ChangeLog b/ChangeLog
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+# 2.1.5 (2023-11-10)
+- bugfix: --flags should be optional!
+- PackageUtils pkgSpecPkgData: error displaying an unparsable pkgid
+
 # 2.1.4 (2023-11-03)
 - spec --standalone should not create subpkgs (regression in 2.1.3)
 - spec: when subpackaging include prof for main exec deps
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -71,7 +71,7 @@
 ## Help output
 `$ cabal-rpm --version`
 ```
-2.1.4
+2.1.5
 ```
 `$ cabal-rpm --help`
 ```
diff --git a/cabal-rpm.cabal b/cabal-rpm.cabal
--- a/cabal-rpm.cabal
+++ b/cabal-rpm.cabal
@@ -1,6 +1,6 @@
 Cabal-version:       1.18
 Name:                cabal-rpm
-Version:             2.1.4
+Version:             2.1.5
 Synopsis:            RPM packaging tool for Haskell Cabal-based packages
 Description:
     This package provides a RPM packaging tool for Haskell Cabal-based packages.
diff --git a/src/Main.hs b/src/Main.hs
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -140,9 +140,10 @@
 
     flags :: Parser Flags
     flags =
-      mapToFlags <$> strOptionWith 'f' "flag" "\"flag1 -flag2 ...\"" "Set or disable Cabal flags"
+      mapToFlags <$> optional (strOptionWith 'f' "flag" "\"flag1 -flag2 ...\"" "Set or disable Cabal flags")
       where
-        mapToFlags cs =
+        mapToFlags Nothing = []
+        mapToFlags (Just cs) =
           let ws = words cs in
             case partition (\w -> head w == '-') ws of
               (ds,es) -> map (\f -> (mkFlagName f,True)) es ++ map (\f -> (mkFlagName (tail f),False)) ds
diff --git a/src/PackageUtils.hs b/src/PackageUtils.hs
--- a/src/PackageUtils.hs
+++ b/src/PackageUtils.hs
@@ -382,7 +382,7 @@
           namever <- (if havePkgname then removePrefix "ghc-" else id) . head
             <$> rpmspec ["--srpm"] (Just "%{name}-%{version}") specFile
           case simpleParse namever of
-            Nothing -> error "pkgid could not be parsed"
+            Nothing -> error' $ "pkgid could not be parsed:" +-+ namever
             Just pkgid -> bringTarball pkgid (Just specFile)
           builddir <- getBuildDir
           let pkgsrcdir = builddir </> namever