diff --git a/compiler/basicTypes/MkId.hs b/compiler/basicTypes/MkId.hs
index 03ab04a24c6c8bcddce3a1c5d38a32ad6fcfda80..87e40dd62f79952a537a7a62ed7d9b0747331fae 100644
--- a/compiler/basicTypes/MkId.hs
+++ b/compiler/basicTypes/MkId.hs
@@ -530,7 +530,11 @@ mkDataConRep dflags fam_envs wrap_name mb_bangs data_con
 
              wrap_sig = mkClosedStrictSig wrap_arg_dmds (dataConCPR data_con)
 
-             wrap_arg_dmds = map mk_dmd arg_ibangs
+             wrap_arg_dmds =
+               replicate (length theta) topDmd ++ map mk_dmd arg_ibangs
+               -- Don't forget the dictionary arguments when building
+               -- the strictness signature (#14290).
+
              mk_dmd str | isBanged str = evalDmd
                         | otherwise           = topDmd
 
diff --git a/testsuite/tests/stranal/should_run/T14290.hs b/testsuite/tests/stranal/should_run/T14290.hs
new file mode 100644
index 0000000000000000000000000000000000000000..7093239d4c223ef18fa8a7c4a6258372715fa064
--- /dev/null
+++ b/testsuite/tests/stranal/should_run/T14290.hs
@@ -0,0 +1,17 @@
+{-# LANGUAGE ExistentialQuantification #-}
+module Main (main) where
+
+main :: IO ()
+main = r `seq` return ()
+
+r :: Rec
+r = Rec{ a = error "xxx", b = 3, c = True }
+
+class C t
+instance C Bool
+
+data Rec = forall t. C t => Rec
+  { a :: ()
+  , b :: !Int
+  , c :: t
+  }
diff --git a/testsuite/tests/stranal/should_run/all.T b/testsuite/tests/stranal/should_run/all.T
index 076474608ef23845e9c68a922ed0e6633d000c04..dada8176cbc146e21de076ed506bfeaca9eef960 100644
--- a/testsuite/tests/stranal/should_run/all.T
+++ b/testsuite/tests/stranal/should_run/all.T
@@ -15,3 +15,4 @@ test('T11555a', normal, compile_and_run, [''])
 test('T12368', exit_code(1), compile_and_run, [''])
 test('T12368a', exit_code(1), compile_and_run, [''])
 test('T13380', [expect_broken(13380), exit_code(1)], compile_and_run, [''])
+test('T14290', normal, compile_and_run, [''])