diff --git a/numbat-cli/src/completer.rs b/numbat-cli/src/completer.rs
index cf37199e..572bc55b 100644
--- a/numbat-cli/src/completer.rs
+++ b/numbat-cli/src/completer.rs
@@ -67,7 +67,14 @@ impl Completer for NumbatCompleter {
             }
         });
 
-        let candidates = self.context.lock().unwrap().get_completions_for(word_part);
+        // don't add an opening paren if we're completing after a reverse function call
+        let add_paren = !line[..pos].find("//").is_some();
+
+        let candidates = self
+            .context
+            .lock()
+            .unwrap()
+            .get_completions_for(word_part, add_paren);
 
         Ok((
             pos_word,
diff --git a/numbat/src/lib.rs b/numbat/src/lib.rs
index 35dc3aad..19e8fb42 100644
--- a/numbat/src/lib.rs
+++ b/numbat/src/lib.rs
@@ -190,7 +190,14 @@ impl Context {
         self.print_sorted(units, FormatType::Unit)
     }
 
-    pub fn get_completions_for<'a>(&self, word_part: &'a str) -> impl Iterator<Item = String> + 'a {
+    /// Gets completions for the given word_part
+    ///
+    /// If `add_paren` is true, then an opening paren will be added to the end of function names
+    pub fn get_completions_for<'a>(
+        &self,
+        word_part: &'a str,
+        add_paren: bool,
+    ) -> impl Iterator<Item = String> + 'a {
         const COMMON_METRIC_PREFIXES: &[&str] = &[
             "pico", "nano", "micro", "milli", "centi", "kilo", "mega", "giga", "tera",
         ];
@@ -211,7 +218,11 @@ impl Context {
             }
 
             for function in self.function_names() {
-                words.push(format!("{}(", function));
+                if add_paren {
+                    words.push(format!("{}(", function));
+                } else {
+                    words.push(format!("{}", function));
+                }
             }
 
             for dimension in self.dimension_names() {