diff --git a/internal/api/handlers_syncpairs.go b/internal/api/handlers_syncpairs.go
index 79ae23d..61e56e0 100644
--- a/internal/api/handlers_syncpairs.go
+++ b/internal/api/handlers_syncpairs.go
@@ -75,8 +75,8 @@ func (h *SyncPairHandler) Create(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "direction must be push, pull, or mirror")
 		return
 	}
-	if req.SourceMachineID != nil && req.DestMachineID != nil {
-		writeError(w, http.StatusBadRequest, "both source and destination cannot be remote machines; one side must be the server (set one MachineID to null)")
+	if req.SourceMachineID != nil && req.DestMachineID != nil && *req.SourceMachineID == *req.DestMachineID {
+		writeError(w, http.StatusBadRequest, "source and destination cannot be the same machine")
 		return
 	}
 	if req.RsyncFlags == "" {
@@ -131,8 +131,8 @@ func (h *SyncPairHandler) Update(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "direction must be push, pull, or mirror")
 		return
 	}
-	if req.SourceMachineID != nil && req.DestMachineID != nil {
-		writeError(w, http.StatusBadRequest, "both source and destination cannot be remote machines; one side must be the server (set one MachineID to null)")
+	if req.SourceMachineID != nil && req.DestMachineID != nil && *req.SourceMachineID == *req.DestMachineID {
+		writeError(w, http.StatusBadRequest, "source and destination cannot be the same machine")
 		return
 	}
 
diff --git a/web/src/pages/SyncPairs.tsx b/web/src/pages/SyncPairs.tsx
index d21f398..4e57a03 100644
--- a/web/src/pages/SyncPairs.tsx
+++ b/web/src/pages/SyncPairs.tsx
@@ -111,6 +111,14 @@ export default function SyncPairs() {
       toast.error('Source and destination paths are required');
       return;
     }
+    if (
+      form.source_machine_id !== null &&
+      form.dest_machine_id !== null &&
+      form.source_machine_id === form.dest_machine_id
+    ) {
+      toast.error('Source and destination cannot be the same machine');
+      return;
+    }
     setLoading(true);
     try {
       await api(form.id ? `/api/sync-pairs/${form.id}` : '/api/sync-pairs', {
@@ -325,6 +333,9 @@ export default function SyncPairs() {
                       ))}
                     </SelectContent>
                   </Select>
+                  <p className="text-xs text-fg-subtle">
+                    Where the data lives. Pick <span className="font-medium">Local server</span> if it&apos;s on this machine, otherwise the remote machine holding the data.
+                  </p>
                 </div>
                 <div className="space-y-1.5">
                   <Label htmlFor="sp-dest-machine">Dest Machine</Label>
@@ -346,6 +357,9 @@ export default function SyncPairs() {
                       ))}
                     </SelectContent>
                   </Select>
+                  <p className="text-xs text-fg-subtle">
+                    Where to copy the data. Can be the same machine (no-op) or any remote. Remote-to-remote is supported.
+                  </p>
                 </div>
               </div>
               <div className="grid grid-cols-2 gap-3">