diff --git a/scripts/build/cc/gcc.sh b/scripts/build/cc/gcc.sh
index cccd654b..39c70bb6 100644
--- a/scripts/build/cc/gcc.sh
+++ b/scripts/build/cc/gcc.sh
@@ -608,6 +608,9 @@ do_gcc_core_backend() {
         cflags_for_target="${cflags_for_target} -idirafter ${CT_HEADERS_DIR}"
     fi
 
+    # Assume '-O2' by default for building target libraries.
+    cflags_for_target="-g -O2 ${cflags_for_target}"
+
     # Use --with-local-prefix so older gccs don't look in /usr/local (http://gcc.gnu.org/PR10532).
     # Pass only user-specified CFLAGS/LDFLAGS in CFLAGS_FOR_TARGET/LDFLAGS_FOR_TARGET: during
     # the build of, for example, libatomic, GCC tried to compile multiple variants for runtime
@@ -936,6 +939,7 @@ do_gcc_backend() {
     local lang_list
     local cflags
     local cflags_for_build
+    local cflags_for_target
     local ldflags
     local build_manuals
     local exec_prefix
@@ -1200,8 +1204,9 @@ do_gcc_backend() {
 
     CT_DoLog DEBUG "Extra config passed: '${extra_config[*]}'"
 
-    # We may need to modify host/build CFLAGS separately below
+    # We may need to modify host/build/target CFLAGS separately below
     cflags_for_build="${cflags}"
+    cflags_for_target="${CT_TARGET_CFLAGS}"
 
     # Clang's default bracket-depth is 256, and building GCC
     # requires somewhere between 257 and 512.
@@ -1217,6 +1222,9 @@ do_gcc_backend() {
         fi
     fi
 
+    # Assume '-O2' by default for building target libraries.
+    cflags_for_target="-g -O2 ${cflags_for_target}"
+
     # NB: not using CT_ALL_TARGET_CFLAGS/CT_ALL_TARGET_LDFLAGS here!
     # See do_gcc_core_backend for explanation.
     CT_DoExecLog CFG                                   \
@@ -1226,8 +1234,8 @@ do_gcc_backend() {
     CXXFLAGS="${cflags}"                               \
     CXXFLAGS_FOR_BUILD="${cflags_for_build}"           \
     LDFLAGS="${final_LDFLAGS[*]}"                      \
-    CFLAGS_FOR_TARGET="${CT_TARGET_CFLAGS}"            \
-    CXXFLAGS_FOR_TARGET="${CT_TARGET_CFLAGS}"          \
+    CFLAGS_FOR_TARGET="${cflags_for_target}"           \
+    CXXFLAGS_FOR_TARGET="${cflags_for_target}"         \
     LDFLAGS_FOR_TARGET="${CT_TARGET_LDFLAGS}"          \
     ${CONFIG_SHELL}                                    \
     "${CT_SRC_DIR}/gcc/configure"                      \