diff --git a/src/klibc/SConscript b/src/klibc/SConscript
index ce214ad1059d..7ea41b6aec31 100644
--- a/src/klibc/SConscript
+++ b/src/klibc/SConscript
@@ -1,5 +1,6 @@
 from building import *
 import os
+import rtconfig
 
 cwd = GetCurrentDir()
 src = ['kerrno.c', 'kstdio.c', 'kstring.c']
@@ -13,7 +14,18 @@ if not GetDepend(['RT_KLIBC_USING_LIBC_VSNPRINTF']):
 if not GetDepend(['RT_KLIBC_USING_LIBC_VSSCANF']):
     src += ['rt_vsscanf.c']
 
-group = DefineGroup('Libc', src, depend = [''])
+# at -O2/-Os, GCC recognises the byte loops used by rt_memset()/rt_memcpy()/
+# rt_memmove() in kstring.c and turns them into calls to memset()/memcpy()/
+# memmove(). Those symbols do not exist on targets built without a C library,
+# so the firmware fails to link (see issue #6128). Keep the loops here.
+group_args = {'depend': ['']}
+if rtconfig.CROSS_TOOL == 'gcc' and not GetOption('clang-analyzer'):
+    # Do not pass LOCAL_CFLAGS in --clang-analyzer builds: building.py replaces
+    # CFLAGS with a list there, and local_group() concatenates it with this
+    # string, which raises TypeError and stops the static analysis.
+    group_args['LOCAL_CFLAGS'] = ' -fno-tree-loop-distribute-patterns'
+
+group = DefineGroup('Libc', src, **group_args)
 
 list = os.listdir(cwd)
 for item in list: