diff --git a/sandboxed_api/tools/clang_generator/CMakeLists.txt b/sandboxed_api/tools/clang_generator/CMakeLists.txt
index 0f38c15..c134e76 100644
--- a/sandboxed_api/tools/clang_generator/CMakeLists.txt
+++ b/sandboxed_api/tools/clang_generator/CMakeLists.txt
@@ -63,3 +63,18 @@ target_link_libraries(sapi_generator_tool PRIVATE
   sapi::generator
 )
 
+if(SAPI_ENABLE_TESTS)
+  add_executable(sapi_generator_test
+    emitter_test.cc
+  )
+  target_link_libraries(sapi_generator_test PRIVATE
+    absl::memory
+    benchmark
+    sapi::sapi
+    sapi::generator
+    sapi::status
+    sapi::status_matchers
+    sapi::test_main
+  )
+  gtest_discover_tests(sapi_generator_test)
+endif()
diff --git a/sandboxed_api/tools/clang_generator/emitter.cc b/sandboxed_api/tools/clang_generator/emitter.cc
index 035a744..48433de 100644
--- a/sandboxed_api/tools/clang_generator/emitter.cc
+++ b/sandboxed_api/tools/clang_generator/emitter.cc
@@ -110,15 +110,17 @@ std::string GetIncludeGuard(absl::string_view filename) {
     return absl::StrCat(
         // Copybara will transform the string. This is intentional.
         "SANDBOXED_API_GENERATED_HEADER_",
-        absl::Hex(absl::Uniform<uint64_t>(*bit_gen), absl::kZeroPad16), "_");
+        absl::AsciiStrToUpper(absl::StrCat(
+            absl::Hex(absl::Uniform<uint64_t>(*bit_gen), absl::kZeroPad16))),
+        "_");
   }
 
-  constexpr absl::string_view kUnderscorePrefix = "SAPI";
+  constexpr absl::string_view kUnderscorePrefix = "SAPI_";
   std::string guard;
   guard.reserve(filename.size() + kUnderscorePrefix.size() + 1);
   for (auto c : filename) {
     if (absl::ascii_isalpha(c)) {
-      guard += c;
+      guard += absl::ascii_toupper(c);
       continue;
     }
     if (guard.empty()) {
diff --git a/sandboxed_api/tools/clang_generator/emitter.h b/sandboxed_api/tools/clang_generator/emitter.h
index c9a267c..42ba92d 100644
--- a/sandboxed_api/tools/clang_generator/emitter.h
+++ b/sandboxed_api/tools/clang_generator/emitter.h
@@ -28,7 +28,7 @@
 namespace sapi {
 
 // Constructs an include guard name for the given filename. The name is of the
-// same for as the include guards in this project.
+// same form as the include guards in this project.
 // For example,
 //   sandboxed_api/examples/zlib/zlib-sapi.sapi.h
 // will be mapped to
diff --git a/sandboxed_api/tools/clang_generator/emitter_test.cc b/sandboxed_api/tools/clang_generator/emitter_test.cc
new file mode 100644
index 0000000..7956df1
--- /dev/null
+++ b/sandboxed_api/tools/clang_generator/emitter_test.cc
@@ -0,0 +1,58 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "sandboxed_api/tools/clang_generator/emitter.h"
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/strings/string_view.h"
+#include "sandboxed_api/util/status_matchers.h"
+
+namespace sapi {
+namespace {
+
+using ::testing::MatchesRegex;
+using ::testing::StrEq;
+using ::testing::StrNe;
+
+TEST(IncludeGuard, CreatesRandomizedGuardForEmptyFilename) {
+  // Copybara will transform the string. This is intentional.
+  constexpr absl::string_view kGeneratedHeaderPrefix =
+      "SANDBOXED_API_GENERATED_HEADER_";
+
+  const std::string include_guard = GetIncludeGuard("");
+  EXPECT_THAT(include_guard, MatchesRegex(absl::StrCat(kGeneratedHeaderPrefix,
+                                                       R"([0-9A-F]+_)")));
+
+  EXPECT_THAT(GetIncludeGuard(""), StrNe(include_guard));
+}
+
+TEST(IncludeGuard, BasicFunctionality) {
+  EXPECT_THAT(GetIncludeGuard("boost/graph/compressed_sparse_row_graph.hpp"),
+              StrEq("BOOST_GRAPH_COMPRESSED_SPARSE_ROW_GRAPH_HPP_"));
+
+  // "SAPI_" prefix is there to avoid generating guards starting with "_"
+  EXPECT_THAT(GetIncludeGuard("/usr/include/unistd.h"),
+              StrEq("SAPI_USR_INCLUDE_UNISTD_H_"));
+}
+
+TEST(IncludeGuard, AvoidReservedIdentifiers) {
+  EXPECT_THAT(GetIncludeGuard("9p.h"), StrEq("SAPI_9P_H_"));
+  EXPECT_THAT(GetIncludeGuard("double__under.h"), StrEq("DOUBLE_UNDER_H_"));
+  EXPECT_THAT(GetIncludeGuard("_single.h"), StrEq("SAPI_SINGLE_H_"));
+  EXPECT_THAT(GetIncludeGuard("__double.h"), StrEq("SAPI_DOUBLE_H_"));
+}
+
+}  // namespace
+}  // namespace sapi