diff --git a/src/components/common/UserSearchPicker.tsx b/src/components/common/UserSearchPicker.tsx
index 5c4fa05..57d82cf 100644
--- a/src/components/common/UserSearchPicker.tsx
+++ b/src/components/common/UserSearchPicker.tsx
@@ -12,12 +12,14 @@ export function UserSearchPicker({
   selectedUser,
   onSelect,
   excludeIds,
+  excludePlatformAdmins,
   label,
   placeholder,
 }: {
   selectedUser: UserListResponse | null
   onSelect: (user: UserListResponse | null) => void
   excludeIds?: string[]
+  excludePlatformAdmins?: boolean
   label?: string
   placeholder?: string
 }) {
@@ -68,9 +70,11 @@ export function UserSearchPicker({
     return () => document.removeEventListener("mousedown", handleClickOutside)
   }, [])
 
-  const filtered = excludeIds
-    ? results.filter((u) => !excludeIds.includes(u.id))
-    : results
+  const filtered = results.filter(
+    (u) =>
+      !(excludePlatformAdmins && u.is_platform_admin) &&
+      !excludeIds?.includes(u.id),
+  )
 
   return (
     <div ref={containerRef} className="space-y-1.5">
@@ -129,7 +133,9 @@ export function UserSearchPicker({
                 </div>
               ) : filtered.length === 0 ? (
                 <p className="text-sm text-verde/50 text-center py-4">
-                  {results.length > 0 && excludeIds ? "All results already added" : "No users found"}
+                  {results.length > 0
+                    ? "All matching users are already added or unavailable"
+                    : "No users found"}
                 </p>
               ) : (
                 filtered.map((user) => (
diff --git a/src/components/pages/ProjectAccessTab.tsx b/src/components/pages/ProjectAccessTab.tsx
index 3613d16..9bd9081 100644
--- a/src/components/pages/ProjectAccessTab.tsx
+++ b/src/components/pages/ProjectAccessTab.tsx
@@ -322,6 +322,8 @@ export function ProjectAccessTab({ projectId }: { projectId: string }) {
         ?.status
       if (status === 409) {
         toast.error("This user already has access to the project")
+      } else if (status === 400) {
+        toast.error("Platform admins can't be added to a project")
       } else {
         toast.error("Failed to grant user access")
       }
@@ -420,6 +422,7 @@ export function ProjectAccessTab({ projectId }: { projectId: string }) {
                 selectedUser={selectedUser}
                 onSelect={setSelectedUser}
                 excludeIds={userAccess.map((u) => u.user_id)}
+                excludePlatformAdmins
                 label="User"
                 placeholder="Search users by email or name..."
               />