diff --git a/include/cxx/cmath b/include/cxx/cmath
index 314f0900ac1..719e625324f 100644
--- a/include/cxx/cmath
+++ b/include/cxx/cmath
@@ -30,7 +30,16 @@
 #include <nuttx/config.h>
 #include <nuttx/compiler.h>
 
-#include <math.h>
+#if defined(CONFIG_LIBM_TOOLCHAIN)
+/* In toolchain libm mode, use toolchain <cmath> so it can include_next the
+ * matching C math.h header and populate std::* consistently.
+ */
+
+#  include_next <cmath>
+
+#else
+
+#  include <math.h>
 
 #undef signbit
 #undef fpclassify
@@ -222,4 +231,6 @@ namespace std
 
 }
 
+#endif
+
 #endif // __INCLUDE_CXX_CMATH