diff --git a/stm/mpconfigport.h b/stm/mpconfigport.h
index fd7af29d27..1d79243f9b 100644
--- a/stm/mpconfigport.h
+++ b/stm/mpconfigport.h
@@ -21,6 +21,14 @@ typedef float machine_float_t;
 
 machine_float_t machine_sqrt(machine_float_t x);
 
+// There is no classical C heap in bare-metal ports, only Python
+// garbage-collected heap. For completeness, emulate C heap via
+// GC heap. Note that MicroPython core never uses malloc() and friends,
+// so these defines are mostly to help extension module writers.
+#define malloc gc_alloc
+#define free gc_free
+#define realloc gc_realloc
+
 // board specific definitions
 
 // choose 1 of these boards
diff --git a/stm/std.h b/stm/std.h
index a2bf706176..843ddd8270 100644
--- a/stm/std.h
+++ b/stm/std.h
@@ -2,10 +2,6 @@ typedef unsigned int size_t;
 
 void __assert_func(void);
 
-void *malloc(size_t n);
-void free(void *ptr);
-void *realloc(void *ptr, size_t n);
-
 void *memcpy(void *dest, const void *src, size_t n);
 void *memmove(void *dest, const void *src, size_t n);
 void *memset(void *s, int c, size_t n);