diff --git a/ext/gcc/atomics_c11_cortex.cpp.in b/ext/gcc/atomics_c11.cpp.in
similarity index 99%
rename from ext/gcc/atomics_c11_cortex.cpp.in
rename to ext/gcc/atomics_c11.cpp.in
index 63546c329f..46aef8ddb9 100644
--- a/ext/gcc/atomics_c11_cortex.cpp.in
+++ b/ext/gcc/atomics_c11.cpp.in
@@ -24,7 +24,7 @@
 
 using _a8 = uint8_t;
 using _a16 = uint16_t;
-using _a32 = unsigned int;
+using _a32 = {{uint32_t}};
 using _a64 = uint64_t;
 
 // =========================== atomics for >64 bits ===========================
diff --git a/ext/gcc/libstdc++ b/ext/gcc/libstdc++
index 9d10e00470..300290d9ea 160000
--- a/ext/gcc/libstdc++
+++ b/ext/gcc/libstdc++
@@ -1 +1 @@
-Subproject commit 9d10e0047011f4c1e6ef4dbf76aca5e9a340a6f8
+Subproject commit 300290d9eae73795762498a7b9bc4c29c2fd1503
diff --git a/ext/gcc/module_c.lb b/ext/gcc/module_c.lb
index 98f99f5065..8d47cb88e4 100644
--- a/ext/gcc/module_c.lb
+++ b/ext/gcc/module_c.lb
@@ -20,9 +20,9 @@ def init(module):
 
 Refines the C language to make it easier to use on embedded targets.
 
-## ARM Cortex-M
+For AVR and ARMv6-M, C11 atomics are implemented via atomic lock.
 
-For ARMv6-M, C11 atomics are implemented via atomic lock.
+## ARM Cortex-M
 
 Additional compiler options:
 
@@ -32,10 +32,12 @@ Additional compiler options:
 
 def prepare(module, options):
     core = options[":target"].get_driver("core")["type"]
+
     if core.startswith("avr") or core.startswith("cortex-m"):
         module.depends(":architecture:assert")
-        if core.startswith("cortex-m0"):
-            module.depends(":architecture:atomic")
+
+    if core.startswith("avr") or core.startswith("cortex-m0"):
+        module.depends(":architecture:atomic")
 
     return True
 
@@ -46,10 +48,12 @@ def build(env):
 
     env.outbasepath = "modm/ext/gcc"
 
+    if core.startswith("avr") or core.startswith("cortex-m0"):
+        uint32_t = "uint32_t" if core.startswith("avr") else "unsigned int"
+        env.template("atomics_c11.cpp.in", substitutions={"uint32_t": uint32_t})
+
     if core.startswith("cortex-m"):
         env.copy("cabi_cortex.c", "cabi.c")
-        if core.startswith("cortex-m0"):
-            env.template("atomics_c11_cortex.cpp.in")
 
         # Compiler options for targets
         env.collect(":build:linkflags", "--specs=nosys.specs")