diff --git a/CMakeLists.txt b/CMakeLists.txt
index 164f9ff..20db3da 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,5 @@
 cmake_minimum_required(VERSION 3.5)
+include(CheckCXXCompilerFlag)
 
 project(FlashMQ LANGUAGES CXX)
 
@@ -7,7 +8,13 @@ add_definitions(-DOPENSSL_API_COMPAT=0x10100000L)
 set(CMAKE_CXX_STANDARD 11)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
-SET(CMAKE_CXX_FLAGS "-rdynamic -msse4.2")
+SET(CMAKE_CXX_FLAGS "-msse4.2")
+
+check_cxx_compiler_flag("-rdynamic" COMPILER_SUPPORTS_RDYNAMIC)
+if (${COMPILER_SUPPORTS_RDYNAMIC})
+    set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -rdynamic")
+    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -rdynamic")
+endif()
 
 add_compile_options(-Wall)
 
diff --git a/build.sh b/build.sh
index bfb9913..4d00cef 100755
--- a/build.sh
+++ b/build.sh
@@ -10,15 +10,15 @@ fi
 
 BUILD_DIR="FlashMQBuild$BUILD_TYPE"
 
+set -eu
+
 if [[ -e "$BUILD_DIR" ]]; then
-  echo "$BUILD_DIR already exists. Not doing anything. You can run 'make' in it, if you want."
-  exit 1
+  >&2 echo "$BUILD_DIR already exists. You can run 'make' in it, if you want.
+"
+else
+  mkdir "$BUILD_DIR"
 fi
 
-set -e
-set -u
-
-mkdir "$BUILD_DIR"
 cd "$BUILD_DIR"
 
 cmake -DCMAKE_BUILD_TYPE="$BUILD_TYPE" "$thisdir"