diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index e53cab2dc..09b76cb35 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -221,7 +221,16 @@ LocalStore::LocalStore(ref<const Config> config)
        schema upgrade is in progress. */
     if (!config->readOnly) {
         Path globalLockPath = dbDir + "/big-lock";
-        globalLock = openLockFile(globalLockPath.c_str(), true);
+        try {
+            globalLock = openLockFile(globalLockPath.c_str(), true);
+        } catch (SysError & e) {
+            if (e.errNo == EACCES || e.errNo == EPERM) {
+                e.addTrace({},
+                    "This command may have been run as non-root in a single-user Nix installation,\n"
+                    "or the Nix daemon may have crashed.");
+            }
+            throw;
+        }
     }
 
     if (!config->readOnly && !lockFile(globalLock.get(), ltRead, false)) {
diff --git a/tests/functional/read-only-store.sh b/tests/functional/read-only-store.sh
index f6b6eaf32..ea96bba41 100755
--- a/tests/functional/read-only-store.sh
+++ b/tests/functional/read-only-store.sh
@@ -42,7 +42,8 @@ chmod -R -w $TEST_ROOT/var
 
 # Make sure we fail on add operations on the read-only store
 # This is only for adding files that are not *already* in the store
-expectStderr 1 nix-store --add eval.nix | grepQuiet "error: opening lock file '$(readlink -e $TEST_ROOT)/var/nix/db/big-lock'"
+# Should show enhanced error message with helpful context
+expectStderr 1 nix-store --add eval.nix | grepQuiet "This command may have been run as non-root in a single-user Nix installation"
 expectStderr 1 nix-store --store local?read-only=true --add eval.nix | grepQuiet "Permission denied"
 
 # Test the same operations from before should again succeed