diff --git a/crates/ra_ide_api/src/symbol_index.rs b/crates/ra_ide_api/src/symbol_index.rs
index 6baeabde68..6184ad3ec3 100644
--- a/crates/ra_ide_api/src/symbol_index.rs
+++ b/crates/ra_ide_api/src/symbol_index.rs
@@ -138,7 +138,7 @@ impl SymbolIndex {
     }
 
     pub(crate) fn memory_size(&self) -> usize {
-        self.map.as_fst().size() * self.symbols.len() * mem::size_of::<FileSymbol>()
+        self.map.as_fst().size() + self.symbols.len() * mem::size_of::<FileSymbol>()
     }
 
     pub(crate) fn for_files(