diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1d390aa..30cef2f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -135,6 +135,10 @@
         FORCE)
 endif()
 
+# Make MBEDTLS_CONFIG_FILE and MBEDTLS_USER_CONFIG_FILE into PATHs
+set(MBEDTLS_CONFIG_FILE "" CACHE FILEPATH "Mbed TLS config file (overrides default).")
+set(MBEDTLS_USER_CONFIG_FILE "" CACHE FILEPATH "Mbed TLS user config file (appended to default).")
+
 # Create a symbolic link from ${base_name} in the binary directory
 # to the corresponding path in the source directory.
 # Note: Copies the file(s) on Windows.
@@ -304,6 +308,20 @@
         PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/include
         PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/library
         PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/3rdparty/everest/include)
+
+    # Pass-through MBEDTLS_CONFIG_FILE and MBEDTLS_USER_CONFIG_FILE
+    if(MBEDTLS_CONFIG_FILE)
+        target_compile_definitions(mbedtls_test
+            PUBLIC MBEDTLS_CONFIG_FILE="${MBEDTLS_CONFIG_FILE}")
+        target_compile_definitions(mbedtls_test_helpers
+            PUBLIC MBEDTLS_CONFIG_FILE="${MBEDTLS_CONFIG_FILE}")
+    endif()
+    if(MBEDTLS_USER_CONFIG_FILE)
+        target_compile_definitions(mbedtls_test
+            PUBLIC MBEDTLS_USER_CONFIG_FILE="${MBEDTLS_USER_CONFIG_FILE}")
+        target_compile_definitions(mbedtls_test_helpers
+            PUBLIC MBEDTLS_USER_CONFIG_FILE="${MBEDTLS_USER_CONFIG_FILE}")
+    endif()
 endif()
 
 if(ENABLE_PROGRAMS)
diff --git a/ChangeLog.d/cmake-pass-through-config-defines.txt b/ChangeLog.d/cmake-pass-through-config-defines.txt
new file mode 100644
index 0000000..6122f37
--- /dev/null
+++ b/ChangeLog.d/cmake-pass-through-config-defines.txt
@@ -0,0 +1,3 @@
+Features
+   * Allow MBEDTLS_CONFIG_FILE and MBEDTLS_USER_CONFIG_FILE to be set by
+     setting the CMake variable of the same name at configuration time.
diff --git a/library/CMakeLists.txt b/library/CMakeLists.txt
index 553569e..a159251 100644
--- a/library/CMakeLists.txt
+++ b/library/CMakeLists.txt
@@ -229,6 +229,15 @@
         PRIVATE ${thirdparty_inc})
     target_compile_definitions(${target}
         PRIVATE ${thirdparty_def})
+    # Pass-through MBEDTLS_CONFIG_FILE and MBEDTLS_USER_CONFIG_FILE
+    if(MBEDTLS_CONFIG_FILE)
+        target_compile_definitions(${target}
+            PUBLIC MBEDTLS_CONFIG_FILE="${MBEDTLS_CONFIG_FILE}")
+    endif()
+    if(MBEDTLS_USER_CONFIG_FILE)
+        target_compile_definitions(${target}
+            PUBLIC MBEDTLS_USER_CONFIG_FILE="${MBEDTLS_USER_CONFIG_FILE}")
+    endif()
     install(TARGETS ${target}
             DESTINATION ${LIB_INSTALL_DIR}
             PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ)
diff --git a/library/net_sockets.c b/library/net_sockets.c
index bdd82ac..2c2a876 100644
--- a/library/net_sockets.c
+++ b/library/net_sockets.c
@@ -90,6 +90,7 @@
 #include <errno.h>
 
 #define IS_EINTR(ret) ((ret) == EINTR)
+#define SOCKET int
 
 #endif /* ( _WIN32 || _WIN32_WCE ) && !EFIX64 && !EFI32 */
 
@@ -494,13 +495,13 @@
     FD_ZERO(&read_fds);
     if (rw & MBEDTLS_NET_POLL_READ) {
         rw &= ~MBEDTLS_NET_POLL_READ;
-        FD_SET(fd, &read_fds);
+        FD_SET((SOCKET) fd, &read_fds);
     }
 
     FD_ZERO(&write_fds);
     if (rw & MBEDTLS_NET_POLL_WRITE) {
         rw &= ~MBEDTLS_NET_POLL_WRITE;
-        FD_SET(fd, &write_fds);
+        FD_SET((SOCKET) fd, &write_fds);
     }
 
     if (rw != 0) {
@@ -608,7 +609,7 @@
     }
 
     FD_ZERO(&read_fds);
-    FD_SET(fd, &read_fds);
+    FD_SET((SOCKET) fd, &read_fds);
 
     tv.tv_sec  = timeout / 1000;
     tv.tv_usec = (timeout % 1000) * 1000;
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 75e5e6b..9eb5c39 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -3412,6 +3412,69 @@
     support_test_cmake_out_of_source
 }
 
+component_build_cmake_custom_config_file () {
+    # Make a copy of config file to use for the in-tree test
+    cp "$CONFIG_H" include/mbedtls_config_in_tree_copy.h
+
+    MBEDTLS_ROOT_DIR="$PWD"
+    mkdir "$OUT_OF_SOURCE_DIR"
+    cd "$OUT_OF_SOURCE_DIR"
+
+    # Build once to get the generated files (which need an intact config file)
+    cmake "$MBEDTLS_ROOT_DIR"
+    make
+
+    msg "build: cmake with -DMBEDTLS_CONFIG_FILE"
+    scripts/config.py -w full_config.h full
+    echo '#error "cmake -DMBEDTLS_CONFIG_FILE is not working."' > "$MBEDTLS_ROOT_DIR/$CONFIG_H"
+    cmake -DGEN_FILES=OFF -DMBEDTLS_CONFIG_FILE=full_config.h "$MBEDTLS_ROOT_DIR"
+    make
+
+    msg "build: cmake with -DMBEDTLS_CONFIG_FILE + -DMBEDTLS_USER_CONFIG_FILE"
+    # In the user config, disable one feature (for simplicity, pick a feature
+    # that nothing else depends on).
+    echo '#undef MBEDTLS_NIST_KW_C' >user_config.h
+
+    cmake -DGEN_FILES=OFF -DMBEDTLS_CONFIG_FILE=full_config.h -DMBEDTLS_USER_CONFIG_FILE=user_config.h "$MBEDTLS_ROOT_DIR"
+    make
+    not programs/test/query_compile_time_config MBEDTLS_NIST_KW_C
+
+    rm -f user_config.h full_config.h
+
+    cd "$MBEDTLS_ROOT_DIR"
+    rm -rf "$OUT_OF_SOURCE_DIR"
+
+    # Now repeat the test for an in-tree build:
+
+    # Restore config for the in-tree test
+    mv include/mbedtls_config_in_tree_copy.h "$CONFIG_H"
+
+    # Build once to get the generated files (which need an intact config)
+    cmake .
+    make
+
+    msg "build: cmake (in-tree) with -DMBEDTLS_CONFIG_FILE"
+    scripts/config.py -w full_config.h full
+    echo '#error "cmake -DMBEDTLS_CONFIG_FILE is not working."' > "$MBEDTLS_ROOT_DIR/$CONFIG_H"
+    cmake -DGEN_FILES=OFF -DMBEDTLS_CONFIG_FILE=full_config.h .
+    make
+
+    msg "build: cmake (in-tree) with -DMBEDTLS_CONFIG_FILE + -DMBEDTLS_USER_CONFIG_FILE"
+    # In the user config, disable one feature (for simplicity, pick a feature
+    # that nothing else depends on).
+    echo '#undef MBEDTLS_NIST_KW_C' >user_config.h
+
+    cmake -DGEN_FILES=OFF -DMBEDTLS_CONFIG_FILE=full_config.h -DMBEDTLS_USER_CONFIG_FILE=user_config.h .
+    make
+    not programs/test/query_compile_time_config MBEDTLS_NIST_KW_C
+
+    rm -f user_config.h full_config.h
+}
+support_build_cmake_custom_config_file () {
+    support_test_cmake_out_of_source
+}
+
+
 component_test_zeroize () {
     # Test that the function mbedtls_platform_zeroize() is not optimized away by
     # different combinations of compilers and optimization flags by using an