diff --git a/src/download-via-ssh/download-via-ssh.cc b/src/download-via-ssh/download-via-ssh.cc
index 5aa1e00ee3..dee4fd78c9 100644
--- a/src/download-via-ssh/download-via-ssh.cc
+++ b/src/download-via-ssh/download-via-ssh.cc
@@ -89,7 +89,7 @@ static void query(std::pair<FdSink, FdSource> & pipes) {
                 std::cout << readLongLong(pipes.second) << std::endl;
             }
         } else
-            throw Error(format("Unknown substituter query `%1%'") % cmd);
+            throw Error(format("unknown substituter query `%1%'") % cmd);
         std::cout << std::endl;
     }
 }
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index 638d244988..038f099649 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -888,7 +888,7 @@ static void opServe(Strings opFlags, Strings opArgs)
                         }
                         break;
                     default:
-                        throw Error(format("Unknown serve query `%1%'") % cmd);
+                        throw Error(format("unknown serve query `%1%'") % cmd);
                 }
                 out.flush();
             }
@@ -897,7 +897,7 @@ static void opServe(Strings opFlags, Strings opArgs)
             dumpPath(readString(in), out);
             break;
         default:
-            throw Error(format("Unknown serve command `%1%'") % cmd);
+            throw Error(format("unknown serve command `%1%'") % cmd);
     }
 }