diff --git a/llvm/lib/FileCheck/FileCheck.cpp b/llvm/lib/FileCheck/FileCheck.cpp
--- a/llvm/lib/FileCheck/FileCheck.cpp
+++ b/llvm/lib/FileCheck/FileCheck.cpp
@@ -1424,6 +1424,14 @@
   // Sort variable captures by the order in which they matched the input.
   // Ranges shouldn't be overlapping, so we can just compare the start.
   llvm::sort(VarCaptures, [](const VarCapture &A, const VarCapture &B) {
+#ifdef EXPENSIVE_CHECKS
+    // When _GLIBCXX_DEBUG is enabled it will call the compare function
+    // with the first item as both sides to check that it is irreflexive
+    // (!(a<a) must be true). Which would otherwise make us think that a
+    // single capture overlaps with itself.
+    if (&A == &B)
+      return false;
+#endif
     assert(A.Range.Start != B.Range.Start &&
            "unexpected overlapping variable captures");
     return A.Range.Start.getPointer() < B.Range.Start.getPointer();