diff --git a/src/libutil/namespaces.cc b/src/libutil/namespaces.cc
index f66accb10..dec3a7189 100644
--- a/src/libutil/namespaces.cc
+++ b/src/libutil/namespaces.cc
@@ -8,31 +8,31 @@
 
 namespace nix {
 
+static void diagnoseUserNamespaces()
+{
+    if (!pathExists("/proc/self/ns/user")) {
+        warn("'/proc/self/ns/user' does not exist; your kernel was likely built without CONFIG_USER_NS=y");
+    }
+
+    Path maxUserNamespaces = "/proc/sys/user/max_user_namespaces";
+    if (!pathExists(maxUserNamespaces) ||
+        trim(readFile(maxUserNamespaces)) == "0")
+    {
+        warn("user namespaces appear to be disabled; check '/proc/sys/user/max_user_namespaces'");
+    }
+
+    Path procSysKernelUnprivilegedUsernsClone = "/proc/sys/kernel/unprivileged_userns_clone";
+    if (pathExists(procSysKernelUnprivilegedUsernsClone)
+        && trim(readFile(procSysKernelUnprivilegedUsernsClone)) == "0")
+    {
+        warn("user namespaces appear to be disabled for unprivileged users; check '/proc/sys/kernel/unprivileged_userns_clone'");
+    }
+}
+
 bool userNamespacesSupported()
 {
     static auto res = [&]() -> bool
     {
-        if (!pathExists("/proc/self/ns/user")) {
-            debug("'/proc/self/ns/user' does not exist; your kernel was likely built without CONFIG_USER_NS=y");
-            return false;
-        }
-
-        Path maxUserNamespaces = "/proc/sys/user/max_user_namespaces";
-        if (!pathExists(maxUserNamespaces) ||
-            trim(readFile(maxUserNamespaces)) == "0")
-        {
-            debug("user namespaces appear to be disabled; check '/proc/sys/user/max_user_namespaces'");
-            return false;
-        }
-
-        Path procSysKernelUnprivilegedUsernsClone = "/proc/sys/kernel/unprivileged_userns_clone";
-        if (pathExists(procSysKernelUnprivilegedUsernsClone)
-            && trim(readFile(procSysKernelUnprivilegedUsernsClone)) == "0")
-        {
-            debug("user namespaces appear to be disabled; check '/proc/sys/kernel/unprivileged_userns_clone'");
-            return false;
-        }
-
         try {
             Pid pid = startProcess([&]()
             {
@@ -44,7 +44,8 @@ bool userNamespacesSupported()
             auto r = pid.wait();
             assert(!r);
         } catch (SysError & e) {
-            debug("user namespaces do not work on this system: %s", e.msg());
+            warn("user namespaces do not work on this system: %s", e.msg());
+            diagnoseUserNamespaces();
             return false;
         }