diff --git a/CHANGELOG.md b/CHANGELOG.md
index afcf04e3..0ef30d99 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
 * Rename project to http-bench
 * Fix flat_streambuf
 * Add ub sanitizer blacklist
+* Add -funsigned-char to asan build target
 
 WebSocket:
 
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 01cbf44b..b0156411 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -117,7 +117,7 @@ if ("${VARIANT}" STREQUAL "coverage")
 
 elseif ("${VARIANT}" STREQUAL "asan")
     set(CMAKE_CXX_FLAGS
-      "${CMAKE_CXX_FLAGS} -fsanitize=address -fno-omit-frame-pointer")
+      "${CMAKE_CXX_FLAGS} -funsigned-char -fsanitize=address -fno-omit-frame-pointer")
     set (CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -fsanitize=address")
     set(CMAKE_BUILD_TYPE RELWITHDEBINFO)
 
diff --git a/Jamroot b/Jamroot
index 40d3f770..11bb39d5 100644
--- a/Jamroot
+++ b/Jamroot
@@ -64,7 +64,7 @@ variant asan
   :
     release
   :
-    <cxxflags>"-fsanitize=address -fno-omit-frame-pointer"
+    <cxxflags>"-funsigned-char -fsanitize=address -fno-omit-frame-pointer"
     <linkflags>"-fsanitize=address"
   ;