diff --git a/.circleci/config.yml b/.circleci/config.yml
index 4f720752..a9a16245 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -44,6 +44,19 @@ jobs:
       - run: ./ci/install_bazel.sh
       - run: ./ci/do_ci.sh bazel.test
 
+  # Verify that we can work on architectures that default to use an unsigned char
+  # See https://github.com/lightstep/lightstep-tracer-cpp/issues/246
+  #     https://github.com/lightstep/lightstep-tracer-cpp/pull/245
+  unsigned_char_test:
+    resource_class: xlarge
+    docker:
+      - image: ubuntu:18.04
+    steps:
+      - checkout
+      - run: ./ci/setup_build_environment.sh
+      - run: ./ci/install_bazel.sh
+      - run: ./ci/do_ci.sh bazel.unsigned_char.test
+
   asan:
     resource_class: xlarge
     docker:
@@ -294,6 +307,7 @@ workflows:
       - cmake_no_grpc
       - cmake_with_grpc
       - test
+      - unsigned_char_test
       - asan
       - tsan
       - windows
diff --git a/ci/do_ci.sh b/ci/do_ci.sh
index 89a6ff59..83827ec4 100755
--- a/ci/do_ci.sh
+++ b/ci/do_ci.sh
@@ -79,6 +79,10 @@ elif [[ "$1" == "bazel.test" ]]; then
   bazel build -c dbg $BAZEL_OPTIONS -- //... -//benchmark/...
   bazel test -c dbg $BAZEL_TEST_OPTIONS //...
   exit 0
+elif [[ "$1" == "bazel.unsigned_char.test" ]]; then
+  bazel build -c dbg --copt -funsigned-char $BAZEL_OPTIONS -- //... -//benchmark/...
+  bazel test -c dbg --copt -funsigned-char $BAZEL_TEST_OPTIONS //...
+  exit 0
 elif [[ "$1" == "bazel.asan" ]]; then
   setup_clang_toolchain
   bazel test -c dbg \
diff --git a/src/common/utility.cpp b/src/common/utility.cpp
index 3c97a1da..dda85bca 100644
--- a/src/common/utility.cpp
+++ b/src/common/utility.cpp
@@ -51,7 +51,8 @@ timeval ToTimeval(std::chrono::microseconds microseconds) {
 static void WriteEscapedString(std::ostringstream& writer,
                                opentracing::string_view s) {
   writer << '"';
-  for (char c : s) {
+  for (auto c_prime : s) {
+    auto c = static_cast<signed char>(c_prime);
     switch (c) {
       case '"':
         writer << R"(\")";
@@ -72,7 +73,8 @@ static void WriteEscapedString(std::ostringstream& writer,
         writer << R"(\t)";
         break;
       default:
-        if ('\x00' <= c && c <= '\x1f') {
+        if (static_cast<signed char>('\x00') <= c &&
+            c <= static_cast<signed char>('\x1f')) {
           writer << R"(\u)";
           writer << std::hex << std::setw(4) << std::setfill('0')
                  << static_cast<int>(c);