diff --git a/Cargo.lock b/Cargo.lock
index 261cd81b2c7..5d8ccb8eced 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -5050,6 +5050,7 @@ dependencies = [
  "derive_more",
  "fxhash",
  "log",
+ "new_debug_unreachable",
  "phf",
  "phf_codegen",
  "precomputed-hash",
diff --git a/components/selectors/Cargo.toml b/components/selectors/Cargo.toml
index bb9efec3a05..884f8c009ac 100644
--- a/components/selectors/Cargo.toml
+++ b/components/selectors/Cargo.toml
@@ -25,6 +25,7 @@ cssparser = "0.29"
 derive_more = "0.99"
 fxhash = "0.2"
 log = "0.4"
+new_debug_unreachable = "1"
 phf = "0.10"
 precomputed-hash = "0.1"
 servo_arc = { version = "0.2", path = "../servo_arc" }
diff --git a/components/selectors/matching.rs b/components/selectors/matching.rs
index 1628e53b890..c41ff0d362f 100644
--- a/components/selectors/matching.rs
+++ b/components/selectors/matching.rs
@@ -9,6 +9,7 @@ use crate::parser::{AncestorHashes, Combinator, Component, LocalName};
 use crate::parser::{NonTSPseudoClass, Selector, SelectorImpl, SelectorIter, SelectorList};
 use crate::tree::Element;
 use bitflags::bitflags;
+use debug_unreachable::debug_unreachable;
 use log::debug;
 use smallvec::SmallVec;
 use std::borrow::Borrow;
@@ -832,7 +833,9 @@ where
             }
             true
         }),
-        Component::Combinator(_) => unreachable!(),
+        Component::Combinator(_) => unsafe {
+            debug_unreachable!("Shouldn't try to selector-match combinators")
+        },
     }
 }