diff --git a/crates/repl_cli/src/repl_state.rs b/crates/repl_cli/src/repl_state.rs
index f3bb1acf5b..a1dcf38fc3 100644
--- a/crates/repl_cli/src/repl_state.rs
+++ b/crates/repl_cli/src/repl_state.rs
@@ -214,9 +214,34 @@ impl ReplState {
             }
         };
 
-        // TODO filter out UNUSED warnings for all past_def_ident entries
-        // TODO allow turning off printing of warnings
-        format_output(output, problems)
+        format_output(output, problems, |warning| {
+            // Filter out UNUSED warnings for entries in past_def_idents,
+            // since otherwise those are totally unhelpful and very annoying!
+            //
+            // Obviously doing string matching on the error message itself is a
+            // brittle and hacky way to do this. It would be nice in the future to
+            // thread the authoritative information through here, but that's
+            // too large a change to justify in the first (already very large)
+            // implementation of the "remembered defs" feature!
+            const UNUSED_DEF_SHORT_PREFIX: &str = "\u{1b}[36m── UNUSED DEFINITION ─";
+            const UNUSED_DEF_FULL_PREFIX:&str  = "\u{1b}[36m── UNUSED DEFINITION ───────────────────────────────────────────────────────────\u{1b}[0m\n\n\u{1b}[34m";
+
+            if warning.starts_with(UNUSED_DEF_SHORT_PREFIX) {
+                let ident_start = &warning[UNUSED_DEF_FULL_PREFIX.len()..];
+
+                if let Some(ident_len) = ident_start.find("\u{1b}[0m") {
+                    let ident = &ident_start[..ident_len];
+
+                    // If this is an unused definition warning for an entry
+                    // in our past_def_idents, filter it out.
+                    if self.past_def_idents.contains(ident) {
+                        return false;
+                    }
+                }
+            }
+
+            true
+        })
     }
 
     fn next_auto_ident(&mut self) -> u64 {
@@ -398,11 +423,20 @@ impl Validator for ReplState {
     }
 }
 
-fn format_output(opt_output: Option<ReplOutput>, problems: Problems) -> String {
+fn format_output<F: FnMut(&&String) -> bool>(
+    opt_output: Option<ReplOutput>,
+    problems: Problems,
+    warning_filter: F,
+) -> String {
     let mut buf = String::new();
 
     // Join all the warnings and errors together with blank lines.
-    for message in problems.warnings.iter().chain(problems.errors.iter()) {
+    for message in problems
+        .warnings
+        .iter()
+        .filter(warning_filter)
+        .chain(problems.errors.iter())
+    {
         if !buf.is_empty() {
             buf.push_str("\n\n");
         }