diff --git a/query-grammar/src/occur.rs b/query-grammar/src/occur.rs
index 62cfb6b57..dfe70c534 100644
--- a/query-grammar/src/occur.rs
+++ b/query-grammar/src/occur.rs
@@ -1,3 +1,6 @@
+use std::fmt;
+use std::fmt::Write;
+
 /// Defines whether a term in a query must be present,
 /// should be present or must not be present.
 #[derive(Debug, Clone, Hash, Copy, Eq, PartialEq)]
@@ -18,7 +21,7 @@ impl Occur {
     /// - `Should` => '?',
     /// - `Must` => '+'
     /// - `Not` => '-'
-    pub fn to_char(self) -> char {
+    fn to_char(self) -> char {
         match self {
             Occur::Should => '?',
             Occur::Must => '+',
@@ -47,3 +50,9 @@ impl Occur {
         }
     }
 }
+
+impl fmt::Display for Occur {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_char(self.to_char())
+    }
+}
diff --git a/query-grammar/src/user_input_ast.rs b/query-grammar/src/user_input_ast.rs
index daf3c9ac2..30452008b 100644
--- a/query-grammar/src/user_input_ast.rs
+++ b/query-grammar/src/user_input_ast.rs
@@ -151,7 +151,7 @@ impl fmt::Debug for UserInputAST {
                 Ok(())
             }
             UserInputAST::Unary(ref occur, ref subquery) => {
-                write!(formatter, "{}({:?})", occur.to_char(), subquery)
+                write!(formatter, "{}({:?})", occur, subquery)
             }
             UserInputAST::Leaf(ref subquery) => write!(formatter, "{:?}", subquery),
         }