diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -4095,9 +4095,26 @@
             << From->getSourceRange();
     }
 
+    // Defer address space conversion to the third conversion.
+    QualType FromPteeType = From->getType()->getPointeeType();
+    QualType ToPteeType = ToType->getPointeeType();
+    QualType NewToType = ToType;
+    if (!FromPteeType.isNull() && !ToPteeType.isNull() &&
+        FromPteeType.getAddressSpace() != ToPteeType.getAddressSpace()) {
+      NewToType = Context.removeAddrSpaceQualType(ToPteeType);
+      NewToType = Context.getAddrSpaceQualType(NewToType,
+                                               FromPteeType.getAddressSpace());
+      if (ToType->isObjCObjectPointerType())
+        NewToType = Context.getObjCObjectPointerType(NewToType);
+      else if (ToType->isBlockPointerType())
+        NewToType = Context.getBlockPointerType(NewToType);
+      else
+        NewToType = Context.getPointerType(NewToType);
+    }
+
     CastKind Kind;
     CXXCastPath BasePath;
-    if (CheckPointerConversion(From, ToType, Kind, BasePath, CStyle))
+    if (CheckPointerConversion(From, NewToType, Kind, BasePath, CStyle))
       return ExprError();
 
     // Make sure we extend blocks if necessary.
@@ -4108,8 +4125,8 @@
       From = E.get();
     }
     if (getLangOpts().allowsNonTrivialObjCLifetimeQualifiers())
-      CheckObjCConversion(SourceRange(), ToType, From, CCK);
-    From = ImpCastExprToType(From, ToType, Kind, VK_RValue, &BasePath, CCK)
+      CheckObjCConversion(SourceRange(), NewToType, From, CCK);
+    From = ImpCastExprToType(From, NewToType, Kind, VK_RValue, &BasePath, CCK)
              .get();
     break;
   }
diff --git a/clang/test/CodeGenOpenCLCXX/addrspace-derived-base.cl b/clang/test/CodeGenOpenCLCXX/addrspace-derived-base.cl
--- a/clang/test/CodeGenOpenCLCXX/addrspace-derived-base.cl
+++ b/clang/test/CodeGenOpenCLCXX/addrspace-derived-base.cl
@@ -69,3 +69,14 @@
   // CHECK: bitcast i8 addrspace(4)* %add.ptr1 to %class.B2 addrspace(4)*
   // CHECK: call {{.*}} @_ZNU3AS42B26getRefEv
 }
+
+// Implicit conversion of derived to base.
+
+void functionWithBaseArgPtr(class B2 *b) {}
+void functionWithBaseArgRef(class B2 &b) {}
+
+void pr43145_4() {
+  Derived d;
+  functionWithBaseArgPtr(&d);
+  functionWithBaseArgRef(d);
+}