diff --git a/dlls/ntdll/atom.c b/dlls/ntdll/atom.c
index 8bb66d33fc4..b8487a259dc 100644
--- a/dlls/ntdll/atom.c
+++ b/dlls/ntdll/atom.c
@@ -54,7 +54,7 @@ static NTSTATUS is_integral_atom( LPCWSTR atomstr, size_t len, RTL_ATOM* pAtom )
     if (HIWORD( atomstr ))
     {
         const WCHAR* ptr = atomstr;
-        if (!len) return STATUS_INVALID_PARAMETER;
+        if (!len) return STATUS_OBJECT_NAME_INVALID;
 
         if (*ptr++ == '#')
         {
@@ -70,7 +70,7 @@ static NTSTATUS is_integral_atom( LPCWSTR atomstr, size_t len, RTL_ATOM* pAtom )
     }
     else atom = LOWORD( atomstr );
 done:
-    if (atom >= MAXINTATOM) return STATUS_INVALID_PARAMETER;
+    if (!atom || atom >= MAXINTATOM) return STATUS_INVALID_PARAMETER;
     *pAtom = atom;
     return STATUS_SUCCESS;
 }
@@ -140,11 +140,11 @@ NTSTATUS WINAPI RtlQueryAtomInAtomTable( RTL_ATOM_TABLE table, RTL_ATOM atom, UL
     {
         if (*len > wlen)
         {
-            *len = wlen;
             memcpy( name, full_name, wlen );
             name[wlen / sizeof(WCHAR)] = 0;
         }
         else status = STATUS_BUFFER_TOO_SMALL;
+        *len = wlen;
     }
 
     TRACE( "%p %x -> %s (%lu)\n",
@@ -196,7 +196,7 @@ NTSTATUS WINAPI RtlAddAtomToAtomTable( RTL_ATOM_TABLE table, const WCHAR* name,
     if (!table) status = STATUS_INVALID_PARAMETER;
     else
     {
-        size_t len = strlenW(name);
+        size_t len = HIWORD(name) ? strlenW(name) : 0;
         status = is_integral_atom( name, len, atom );
         if (status == STATUS_MORE_ENTRIES)
         {
@@ -226,7 +226,7 @@ NTSTATUS WINAPI RtlLookupAtomInAtomTable( RTL_ATOM_TABLE table, const WCHAR* nam
     if (!table) status = STATUS_INVALID_PARAMETER;
     else
     {
-        size_t len = strlenW(name);
+        size_t len = HIWORD(name) ? strlenW(name) : 0;
         status = is_integral_atom( name, len, atom );
         if (status == STATUS_MORE_ENTRIES)
         {
@@ -271,19 +271,19 @@ NTSTATUS WINAPI RtlEmptyAtomTable( RTL_ATOM_TABLE table, BOOLEAN delete_pinned )
  */
 NTSTATUS WINAPI RtlPinAtomInAtomTable( RTL_ATOM_TABLE table, RTL_ATOM atom )
 {
-    NTSTATUS    status = STATUS_INVALID_PARAMETER;
+    NTSTATUS status;
 
-    if (table && atom >= MAXINTATOM)
+    if (!table) return STATUS_INVALID_PARAMETER;
+    if (atom < MAXINTATOM) return STATUS_SUCCESS;
+
+    SERVER_START_REQ( set_atom_information )
     {
-        SERVER_START_REQ( set_atom_information )
-        {
-            req->table = table;
-            req->atom = atom;
-            req->pinned = TRUE;
-            status = wine_server_call( req );
-        }
-        SERVER_END_REQ;
+        req->table = table;
+        req->atom = atom;
+        req->pinned = TRUE;
+        status = wine_server_call( req );
     }
+    SERVER_END_REQ;
 
     return status;
 }
diff --git a/server/atom.c b/server/atom.c
index 83c80702992..52797cac650 100644
--- a/server/atom.c
+++ b/server/atom.c
@@ -253,10 +253,12 @@ static atom_t add_atom( struct atom_table *table, const WCHAR *str, size_t len )
 }
 
 /* delete an atom from the table */
-static void delete_atom( struct atom_table *table, atom_t atom )
+static void delete_atom( struct atom_table *table, atom_t atom, int if_pinned )
 {
     struct atom_entry *entry = get_atom_entry( table, atom );
-    if (entry && !--entry->count)
+    if (!entry) return;
+    if (entry->pinned && !if_pinned) set_error( STATUS_WAS_LOCKED );
+    else if (!--entry->count)
     {
         if (entry->next) entry->next->prev = entry->prev;
         if (entry->prev) entry->prev->next = entry->next;
@@ -328,7 +330,7 @@ int grab_global_atom( atom_t atom )
 /* decrement the ref count of a global atom; used for window properties */
 void release_global_atom( atom_t atom )
 {
-    if (atom >= MIN_STR_ATOM) delete_atom( global_table, atom );
+    if (atom >= MIN_STR_ATOM) delete_atom( global_table, atom, 1 );
 }
 
 /* add a global atom */
@@ -348,7 +350,7 @@ DECL_HANDLER(delete_atom)
     struct atom_table *table = get_table( req->table );
     if (table)
     {
-        delete_atom( table, req->atom );
+        delete_atom( table, req->atom, 0 );
         release_object( table );
     }
 }
@@ -376,7 +378,7 @@ DECL_HANDLER(get_atom_information)
         {
             size_t len = entry->len * sizeof(WCHAR);
             if (len <= get_reply_max_size()) set_reply_data( entry->str, len );
-            else set_error( STATUS_BUFFER_OVERFLOW );
+            else if (get_reply_max_size()) set_error( STATUS_BUFFER_OVERFLOW );
             reply->count = entry->count;
             reply->pinned = entry->pinned;
         }