diff --git a/pkgs/development/haskell-modules/generic-builder.nix b/pkgs/development/haskell-modules/generic-builder.nix
index 96de6ab6d3f..c633310a37a 100644
--- a/pkgs/development/haskell-modules/generic-builder.nix
+++ b/pkgs/development/haskell-modules/generic-builder.nix
@@ -276,7 +276,7 @@ stdenv.mkDerivation ({
 
     echo configureFlags: $configureFlags
     ${setupCommand} configure $configureFlags 2>&1 | ${coreutils}/bin/tee "$NIX_BUILD_TOP/cabal-configure.log"
-    if ${gnugrep}/bin/egrep -q '^Warning:.*depends on multiple versions' "$NIX_BUILD_TOP/cabal-configure.log"; then
+    if ${gnugrep}/bin/egrep -q -z 'Warning:.*depends on multiple versions' "$NIX_BUILD_TOP/cabal-configure.log"; then
       echo >&2 "*** abort because of serious configure-time warning from Cabal"
       exit 1
     fi