diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -146,6 +146,8 @@
   uses the optional USR value when indexing Clang's AST. This value is expected
   to be generated by an external compiler when generating C++ bindings during
   the compilation of the foreign language sources (e.g. Swift).
+- The ``__has_attribute``, ``__has_c_attribute`` and ``__has_cpp_attribute``
+  preprocessor operators now return 1 also for attributes defined by plugins.
 
 Improvements to Clang's diagnostics
 -----------------------------------
diff --git a/clang/examples/Attribute/Attribute.cpp b/clang/examples/Attribute/Attribute.cpp
--- a/clang/examples/Attribute/Attribute.cpp
+++ b/clang/examples/Attribute/Attribute.cpp
@@ -9,6 +9,8 @@
 // Example clang plugin which adds an an annotation to file-scope declarations
 // with the 'example' attribute.
 //
+// This plugin is used by clang/test/Frontend/plugin-attribute tests.
+//
 //===----------------------------------------------------------------------===//
 
 #include "clang/AST/ASTContext.h"
@@ -27,9 +29,10 @@
     // number of arguments. This just illustrates how many arguments a
     // `ParsedAttrInfo` can hold, we will not use that much in this example.
     OptArgs = 15;
-    // GNU-style __attribute__(("example")) and C++-style [[example]] and
+    // GNU-style __attribute__(("example")) and C++/C2x-style [[example]] and
     // [[plugin::example]] supported.
     static constexpr Spelling S[] = {{ParsedAttr::AS_GNU, "example"},
+                                     {ParsedAttr::AS_C2x, "example"},
                                      {ParsedAttr::AS_CXX11, "example"},
                                      {ParsedAttr::AS_CXX11, "plugin::example"}};
     Spellings = S;
diff --git a/clang/lib/Basic/Attributes.cpp b/clang/lib/Basic/Attributes.cpp
--- a/clang/lib/Basic/Attributes.cpp
+++ b/clang/lib/Basic/Attributes.cpp
@@ -2,6 +2,7 @@
 #include "clang/Basic/AttrSubjectMatchRules.h"
 #include "clang/Basic/AttributeCommonInfo.h"
 #include "clang/Basic/IdentifierTable.h"
+#include "clang/Basic/ParsedAttrInfo.h"
 using namespace clang;
 
 static int hasAttributeImpl(AttributeCommonInfo::Syntax Syntax, StringRef Name,
@@ -40,6 +41,11 @@
   if (res)
     return res;
 
+  // Check if any plugin provides this attribute.
+  for (auto &Ptr : getAttributePluginInstances())
+    if (Ptr->hasSpelling(Syntax, Name))
+      return 1;
+
   return 0;
 }
 
diff --git a/clang/test/Frontend/plugin-attribute-pp.cpp b/clang/test/Frontend/plugin-attribute-pp.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/Frontend/plugin-attribute-pp.cpp
@@ -0,0 +1,36 @@
+// RUN: split-file %s %t
+// RUN: %clang -fplugin=%llvmshlibdir/Attribute%pluginext -E %t/has_attr.cpp | FileCheck %t/has_attr.cpp
+// RUN: %clang -fplugin=%llvmshlibdir/Attribute%pluginext -E %t/has_attr.c | FileCheck %t/has_attr.c
+// REQUIRES: plugins, examples
+
+
+//--- has_attr.cpp
+#if __has_attribute (example)
+// CHECK: YES - It did exist
+YES - It did exist
+#endif
+#if __has_cpp_attribute (example)
+// CHECK: YES - It did cpp-exist
+YES - It did cpp-exist
+#endif
+
+#if __has_attribute (doesnt_exist)
+// CHECK-NOT: NO - There is no such attribute
+NO - There is no such attribute
+#endif
+
+
+//--- has_attr.c
+#if __has_attribute (example)
+// CHECK: YES - It did exist
+YES - It did exist
+#endif
+#if __has_c_attribute (example)
+// CHECK: YES - It did c-exist
+YES - It did c-exist
+#endif
+
+#if __has_attribute (doesnt_exist)
+// CHECK-NOT: NO - There is no such attribute
+NO - There is no such attribute
+#endif