diff --git a/ext/c4core b/ext/c4core
index fe1ad5f54..0a5d475c9 160000
--- a/ext/c4core
+++ b/ext/c4core
@@ -1 +1 @@
-Subproject commit fe1ad5f5419ab5f292ed46ab748e608222e513b9
+Subproject commit 0a5d475c9946da68c26b1fe1689daa720d5ca15a
diff --git a/tools/amalgamate.py b/tools/amalgamate.py
index fac992435..5097819b7 100644
--- a/tools/amalgamate.py
+++ b/tools/amalgamate.py
@@ -31,6 +31,11 @@
 #if defined(RYML_SHARED) && !defined(C4CORE_SHARED)
 #define C4CORE_SHARED
 #endif
+
+// workaround for include removal while amalgamating
+// resulting in <stdarg.h> missing in arm-none-eabi-g++
+// https://github.com/biojppm/rapidyaml/issues/193
+#include <stdarg.h>
 """