diff --git a/build-support/macros-and-definitions.cmake b/build-support/macros-and-definitions.cmake
index 89fd6bca5..f974bbd2a 100644
--- a/build-support/macros-and-definitions.cmake
+++ b/build-support/macros-and-definitions.cmake
@@ -159,6 +159,9 @@ macro(process_options)
                                                         STREQUAL "default"
   )
     set(cmakeBuildType relwithdebinfo)
+    string(REPLACE "-O2" "-Os" CMAKE_CXX_FLAGS_RELWITHDEBINFO
+                   "${CMAKE_CXX_FLAGS_RELWITHDEBINFO}"
+    )
     set(CMAKE_CXX_FLAGS_DEFAULT ${CMAKE_CXX_FLAGS_RELWITHDEBINFO})
     add_definitions(-DNS3_BUILD_PROFILE_DEBUG)
   elseif(${cmakeBuildType} STREQUAL "release")
diff --git a/doc/manual/source/working-with-cmake.rst b/doc/manual/source/working-with-cmake.rst
index 9527c0ca4..2d7dc3172 100644
--- a/doc/manual/source/working-with-cmake.rst
+++ b/doc/manual/source/working-with-cmake.rst
@@ -173,7 +173,7 @@ The mapping of the ``ns3`` build profiles into the CMake build types is the foll
 +=========================+========================+===============================+=================================+
 | debug                   | debug                  |                               | -g                              |
 +-------------------------+------------------------+-------------------------------+---------------------------------+
-| default                 | default                |                               | -O2 -g                          |
+| default                 | default                |                               | -Os -g                          |
 +-------------------------+------------------------+-------------------------------+---------------------------------+
 | release                 | release                |                               | -O3                             |
 +-------------------------+------------------------+-------------------------------+---------------------------------+
@@ -235,9 +235,9 @@ build types and output executable and libraries names, which will receive a suff
 +==================+===================+
 | DEBUG            | -g                |
 +------------------+-------------------+
-| DEFAULT          | -O2 -g -DNDEBUG   |
+| DEFAULT          | -Os -g -DNDEBUG   |
 +------------------+-------------------+
-| RELWITHDEBINFO   | -O2 -g -DNDEBUG   |
+| RELWITHDEBINFO   | -Os -g -DNDEBUG   |
 +------------------+-------------------+
 | RELEASE          | -O3 -DNDEBUG      |
 +------------------+-------------------+
@@ -1965,7 +1965,7 @@ Installing the packages can take a while, and it can look like it hanged.
   --
   -- Copying /ns-3-dev/cmake-build-release/_deps/armadillo-src/include/ to /ns-3-dev/cmake-build-release/_deps/armadillo-build/tmp/include/
   -- Generating /ns-3-dev/cmake-build-release/_deps/armadillo-build/tmp/include/config.hpp
-  -- CMAKE_CXX_FLAGS           =  -fsanitize=address,leak,undefined -O2
+  -- CMAKE_CXX_FLAGS           =  -fsanitize=address,leak,undefined -Os
   -- CMAKE_SHARED_LINKER_FLAGS =  -Wl,--no-as-needed
   -- CMAKE_REQUIRED_INCLUDES   = /usr/include;/usr/include/superlu
   --
diff --git a/doc/tutorial/source/getting-started.rst b/doc/tutorial/source/getting-started.rst
index b488bf4c2..136bd2831 100644
--- a/doc/tutorial/source/getting-started.rst
+++ b/doc/tutorial/source/getting-started.rst
@@ -795,7 +795,7 @@ The build profile controls the use of logging, assertions, and compiler optimiza
     | Wrapper  |                                 |                             |                               |                                 |
     | Macro    |                                 |                             |                               |                                 |
     +----------+---------------------------------+-----------------------------+-------------------------------+---------------------------------+
-    | Compiler | ``-Og -g``                      | ``-O2 -g``                  | ``-O3``                       | ``-O3``                         |
+    | Compiler | ``-Og -g``                      | ``-Os -g``                  | ``-O3``                       | ``-O3``                         |
     | Flags    |                                 |                             |                               | ``-march=native``               |
     |          |                                 |                             |                               | ``-mtune=native``               |
     +----------+---------------------------------+-----------------------------+-------------------------------+---------------------------------+