diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 675299aa4cd..c81e024e0e2 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -2687,9 +2687,16 @@ satisfaction_cache
       *slot = entry;
     }
   else
-    /* We shouldn't get here, but if we do, let's just leave 'entry'
-       empty, effectively disabling the cache.  */
-    return;
+    {
+      /* We're evaluating this atom for the first time, and doing so noisily.
+	 This shouldn't happen outside of error recovery situations involving
+	 unstable satisfaction.  Let's just leave 'entry' empty, effectively
+	 disabling the cache, and remove the empty slot.  */
+      gcc_checking_assert (seen_error ());
+      /* Appease hash_table::check_complete_insertion.  */
+      *slot = ggc_alloc<sat_entry> ();
+      sat_cache->clear_slot (slot);
+    }
 }
 
 /* Returns the cached satisfaction result if we have one and we're not
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-pr109752.C b/gcc/testsuite/g++.dg/cpp2a/concepts-pr109752.C
new file mode 100644
index 00000000000..d54ce295e50
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-pr109752.C
@@ -0,0 +1,26 @@
+// PR c++/109752
+// { dg-do compile { target c++20 } }
+
+template <typename _Tp, typename... _Args>
+  inline constexpr bool is_constructible_v = __is_constructible(_Tp, _Args...);
+    template<typename _Tp, typename _Up>
+      concept __weakly_eq_cmp_with
+ = requires(_Tp __t, _Up __u) {    { __u != __t } ; // { dg-error "changed from" }
+ };
+  template<typename _Tp>
+    concept regular =  is_constructible_v<_Tp>  && __weakly_eq_cmp_with<_Tp, _Tp>;
+  template<typename _Iter> concept incrementable = true
+&& regular<_Iter>
+&& requires(_Iter __i) { { __i++ } ;}
+;
+template<typename D>
+struct iterator_interface
+{
+  friend constexpr bool operator>=(D lhs, D rhs) requires __weakly_eq_cmp_with<D, D> { return true; }
+};
+template<typename T>
+struct iterator : iterator_interface<iterator<T>>
+{
+    bool operator==(iterator) const;
+};
+static_assert(incrementable<iterator<int>>); // { dg-error "assert" }