diff --git a/proc/src/proc_command.rs b/proc/src/proc_command.rs
index 48ae0fe..12347ee 100644
--- a/proc/src/proc_command.rs
+++ b/proc/src/proc_command.rs
@@ -144,7 +144,7 @@ impl ToTokens for CommandDef {
             /// mutable pointer to [#state], invoking predefined operations
             /// and optionally returning undo history data.
             impl ::tengri::input::Command<#state> for #command_enum {
-                fn execute (self, state: &mut #state) -> Perhaps<Self> {
+                fn execute (&self, state: &mut #state) -> Perhaps<Self> {
                     match self { #(#implementations)* }
                 }
             }