diff --git a/src/libexpr/tests/error_traces.cc b/src/libexpr/tests/error_traces.cc
index 285651256..1af601ec8 100644
--- a/src/libexpr/tests/error_traces.cc
+++ b/src/libexpr/tests/error_traces.cc
@@ -1084,7 +1084,7 @@ namespace nix {
 
         ASSERT_TRACE1("hashString \"foo\" \"content\"",
                       UsageError,
-                      hintfmt("unknown hash algorithm '%s'", "foo"));
+                      hintfmt("unknown hash algorithm '%s', expect 'md5', 'sha1', 'sha256', or 'sha512'", "foo"));
 
         ASSERT_TRACE2("hashString \"sha256\" {}",
                       TypeError,
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 6d56c1989..251440363 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -401,7 +401,7 @@ HashType parseHashType(std::string_view s)
     if (opt_h)
         return *opt_h;
     else
-        throw UsageError("unknown hash algorithm '%1%'", s);
+        throw UsageError("unknown hash algorithm '%1%', expect 'md5', 'sha1', 'sha256', or 'sha512'", s);
 }
 
 std::string_view printHashType(HashType ht)