diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6ad803aaa..65367731a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -156,6 +156,7 @@ install(FILES
 
 if(HIGHFIVE_EXAMPLES OR HIGHFIVE_UNIT_TESTS)
   include(${CMAKE_CURRENT_SOURCE_DIR}/cmake/HighFiveWarnings.cmake)
+  include(${CMAKE_CURRENT_SOURCE_DIR}/cmake/HighFiveFlags.cmake)
   include(${CMAKE_CURRENT_SOURCE_DIR}/cmake/HighFiveOptionalDependencies.cmake)
 endif()
 
diff --git a/cmake/HighFiveFlags.cmake b/cmake/HighFiveFlags.cmake
new file mode 100644
index 000000000..33be65e9c
--- /dev/null
+++ b/cmake/HighFiveFlags.cmake
@@ -0,0 +1,30 @@
+if(TARGET HighFiveFlags)
+    # Allow multiple `include(HighFiveWarnings)`, which would
+    # attempt to redefine `HighFiveWarnings` and fail without
+    # this check.
+    return()
+endif()
+
+add_library(HighFiveFlags INTERFACE)
+
+if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+    if(HIGHFIVE_MAX_ERRORS)
+        target_compile_options(HighFiveFlags
+            INTERFACE
+            -fmax-errors=${HIGHFIVE_MAX_ERRORS}
+        )
+    endif()
+endif()
+
+if(HIGHFIVE_GLIBCXX_ASSERTIONS)
+    target_compile_definitions(HighFiveFlags INTERFACE -D_GLIBCXX_ASSERTIONS)
+endif()
+
+if(HIGHFIVE_HAS_FRIEND_DECLARATIONS)
+    target_compile_definitions(HighFiveFlags INTERFACE -DHIGHFIVE_HAS_FRIEND_DECLARATIONS=1)
+endif()
+
+if(HIGHFIVE_SANITIZER)
+    target_compile_options(HighFiveFlags INTERFACE -fsanitize=${HIGHFIVE_SANITIZER})
+    target_link_options(HighFiveFlags INTERFACE -fsanitize=${HIGHFIVE_SANITIZER})
+endif()
diff --git a/cmake/HighFiveWarnings.cmake b/cmake/HighFiveWarnings.cmake
index a1dee19dc..2357a97ca 100644
--- a/cmake/HighFiveWarnings.cmake
+++ b/cmake/HighFiveWarnings.cmake
@@ -6,7 +6,6 @@ if(TARGET HighFiveWarnings)
 endif()
 
 add_library(HighFiveWarnings INTERFACE)
-add_library(HighFiveFlags INTERFACE)
 
 if(CMAKE_CXX_COMPILER_ID MATCHES "Clang"
    OR CMAKE_CXX_COMPILER_ID MATCHES "GNU"
@@ -48,11 +47,3 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR CMAKE_CXX_COMPILER_ID MATCHES "GNU")
     endif()
 endif()
 
-if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
-    if(HIGHFIVE_MAX_ERRORS)
-        target_compile_options(HighFiveFlags
-            INTERFACE
-            -fmax-errors=${HIGHFIVE_MAX_ERRORS}
-        )
-    endif()
-endif()