diff --git a/include/swift/AST/Requirement.h b/include/swift/AST/Requirement.h
index b82efc2314206..bcc49f1797269 100644
--- a/include/swift/AST/Requirement.h
+++ b/include/swift/AST/Requirement.h
@@ -198,6 +198,10 @@ class Requirement {
   /// 'T : C' can be satisfied; however, if 'T' already has an unrelated
   /// superclass requirement, 'T : C' cannot be satisfied.
   bool canBeSatisfied() const;
+  
+  /// True if the requirement states a conformance to an invertible protocol
+  /// that is implied by default (such as `Copyable` or `Escapable`.
+  bool isInvertibleProtocolRequirement() const;
 
   /// Linear order on requirements in a generic signature.
   int compare(const Requirement &other) const;
diff --git a/lib/AST/GenericSignature.cpp b/lib/AST/GenericSignature.cpp
index 8fbb654bf30f7..4dfa5d9c0cd3a 100644
--- a/lib/AST/GenericSignature.cpp
+++ b/lib/AST/GenericSignature.cpp
@@ -1282,9 +1282,7 @@ void GenericSignatureImpl::getRequirementsWithInverses(
 
   // Filter out explicit conformances to invertible protocols.
   for (auto req : getRequirements()) {
-    if (req.getKind() == RequirementKind::Conformance &&
-        req.getFirstType()->is<GenericTypeParamType>() &&
-        req.getProtocolDecl()->getInvertibleProtocolKind()) {
+    if (req.isInvertibleProtocolRequirement()) {
       continue;
     }
 
diff --git a/lib/AST/Requirement.cpp b/lib/AST/Requirement.cpp
index 4e6e9b7afe634..6547f61541be2 100644
--- a/lib/AST/Requirement.cpp
+++ b/lib/AST/Requirement.cpp
@@ -205,6 +205,12 @@ bool Requirement::canBeSatisfied() const {
   llvm_unreachable("Bad requirement kind");
 }
 
+bool Requirement::isInvertibleProtocolRequirement() const {
+  return getKind() == RequirementKind::Conformance
+      && getFirstType()->is<GenericTypeParamType>()
+      && getProtocolDecl()->getInvertibleProtocolKind();
+}
+
 /// Determine the canonical ordering of requirements.
 static unsigned getRequirementKindOrder(RequirementKind kind) {
   switch (kind) {
diff --git a/lib/IRGen/GenProto.cpp b/lib/IRGen/GenProto.cpp
index 02d9f10ef2374..4bfaae534bd77 100644
--- a/lib/IRGen/GenProto.cpp
+++ b/lib/IRGen/GenProto.cpp
@@ -2118,24 +2118,30 @@ namespace {
 
       // Compute the inverse requirements from the generic signature where the
       // conformance occurs.
-      SmallVector<Requirement, 2> scratchReqs;
+      SmallVector<Requirement, 2> condReqs;
       SmallVector<InverseRequirement, 2> inverses;
       if (auto genericSig =
               normal->getDeclContext()->getGenericSignatureOfContext()) {
-        genericSig->getRequirementsWithInverses(scratchReqs, inverses);
-        scratchReqs.clear();
+        genericSig->getRequirementsWithInverses(condReqs, inverses);
+      }
+      condReqs.clear();
+
+      for (auto condReq : normal->getConditionalRequirements()) {
+        // We don't need to collect conditional requirements for invertible
+        // protocol requirements here, since they are encoded in the inverse
+        // list above.
+        if (!condReq.isInvertibleProtocolRequirement()) {
+          condReqs.push_back(condReq);
+        }
       }
-
-      auto condReqs = normal->getConditionalRequirements();
       if (condReqs.empty()) {
         // For a protocol P that conforms to another protocol, introduce a
         // conditional requirement for that P's Self: P. This aligns with
         // SILWitnessTable::enumerateWitnessTableConditionalConformances().
         if (auto selfProto = normal->getDeclContext()->getSelfProtocolDecl()) {
           auto selfType = selfProto->getSelfInterfaceType()->getCanonicalType();
-          scratchReqs.emplace_back(RequirementKind::Conformance, selfType,
+          condReqs.emplace_back(RequirementKind::Conformance, selfType,
                                    selfProto->getDeclaredInterfaceType());
-          condReqs = scratchReqs;
         }
 
         if (condReqs.empty() && inverses.empty())
diff --git a/test/IRGen/retrofitted-noncopyable-types-and-external-conformance-extensions.swift b/test/IRGen/retrofitted-noncopyable-types-and-external-conformance-extensions.swift
new file mode 100644
index 0000000000000..c89f6bb63161a
--- /dev/null
+++ b/test/IRGen/retrofitted-noncopyable-types-and-external-conformance-extensions.swift
@@ -0,0 +1,43 @@
+// RUN: %target-swift-frontend -emit-ir %s | %FileCheck --check-prefix=IR %s
+// RUN: %target-run-simple-swift | %FileCheck --check-prefix=EXEC %s
+
+// REQUIRES: executable_test
+
+// The conformance descriptor for Optional: P ought to be encoded as if it
+// were an unconditional conformance. We check this by checking that the
+// global variable type is `%swift.protocol_conformance_descriptor`, indicating
+// that there is no tail matter encoding conditional or inverted requirements.
+
+// IR-LABEL: @"$sxSg4main1PABMc" ={{.*}} constant %swift.protocol_conformance_descriptor {
+
+protocol P /*<implied> : Copyable*/ {
+    func p()
+}
+
+extension Optional: P /*<implied> where T: Copyable */ {
+    func p() {
+        print("conforming optional \(self)")
+    }
+}
+
+@inline(never)
+func cast<T>(value: T) -> (any P)? {
+    return value as? any P
+}
+
+func main() {
+    // EXEC: going to test
+    print("going to test")
+
+    // EXEC-NEXT: conforming optional Optional("test")
+    let x: String? = "test"
+    if let p = cast(value: x) {
+        p.p()
+    } else {
+        print("not a P")
+    }
+
+    // EXEC-NEXT: done testing
+    print("done testing")
+}
+main()