diff --git a/ueforth/esp32/builtins.h b/ueforth/esp32/builtins.h
index a59bf2c..b4b07aa 100644
--- a/ueforth/esp32/builtins.h
+++ b/ueforth/esp32/builtins.h
@@ -62,6 +62,8 @@ static cell_t ResizeFile(cell_t fd, cell_t size);
   OPTIONAL_SPI_FLASH_SUPPORT \
   USER_WORDS
 
+#ifndef SIM_PRINT_ONLY
+
 #define REQUIRED_MEMORY_SUPPORT \
   Y(MALLOC, SET malloc(n0)) \
   Y(SYSFREE, free(a0); DROP) \
@@ -84,6 +86,8 @@ static cell_t ResizeFile(cell_t fd, cell_t size);
   X("Serial.write", SERIAL_WRITE, n0 = Serial.write(b1, n0); NIP) \
   X("Serial.flush", SERIAL_FLUSH, Serial.flush())
 
+#endif
+
 #define REQUIRED_ARDUINO_GPIO_SUPPORT \
   Y(pinMode, pinMode(n1, n0); DROPn(2)) \
   Y(digitalWrite, digitalWrite(n1, n0); DROPn(2)) \
diff --git a/ueforth/esp32/print-builtins.cpp b/ueforth/esp32/print-builtins.cpp
index 9f868cd..71d4bbf 100644
--- a/ueforth/esp32/print-builtins.cpp
+++ b/ueforth/esp32/print-builtins.cpp
@@ -20,12 +20,15 @@
 #include "esp32/options.h"
 #define FLOATING_POINT_LIST
 #define USER_WORDS
+#define REQUIRED_MEMORY_SUPPORT
+#define REQUIRED_SYSTEM_SUPPORT
+#define REQUIRED_SERIAL_SUPPORT
 #include "builtins.h"
 
 #define Y(name, code) X(#name, name, code)
 
 int main() {
-  printf("#define PLATFORM_OPCODE_LIST \\\n");
+  printf("#define PLATFORM_MOCK_OPCODE_LIST \\\n");
 #define X(str, name, code) printf("  X(\"%s\", %s, ) \\\n", str, #name);
   PLATFORM_OPCODE_LIST
 #undef X
diff --git a/ueforth/esp32/sim_main.cpp b/ueforth/esp32/sim_main.cpp
index e21a7b9..6a5e10a 100644
--- a/ueforth/esp32/sim_main.cpp
+++ b/ueforth/esp32/sim_main.cpp
@@ -17,6 +17,38 @@
 #include "common/opcodes.h"
 #include "common/floats.h"
 #include "common/calling.h"
+#include <time.h>
+#include <unistd.h>
+
+#define PLATFORM_OPCODE_LIST \
+  FLOATING_POINT_LIST \
+  REQUIRED_MEMORY_SUPPORT \
+  REQUIRED_SYSTEM_SUPPORT \
+  REQUIRED_SERIAL_SUPPORT \
+  PLATFORM_MOCK_OPCODE_LIST
+
+#define REQUIRED_MEMORY_SUPPORT \
+  Y(MALLOC, SET malloc(n0)) \
+  Y(SYSFREE, free(a0); DROP) \
+  Y(REALLOC, SET realloc(a1, n0); NIP) \
+  Y(heap_caps_malloc, SET malloc(n1); NIP) \
+  Y(heap_caps_free, free(a0); DROP) \
+  Y(heap_caps_realloc, \
+      tos = (cell_t) realloc(a2, n1); NIPn(2))
+
+#define REQUIRED_SYSTEM_SUPPORT \
+  X("MS-TICKS", MS_TICKS, PUSH time(0) * 1000) \
+  X("RAW-YIELD", RAW_YIELD, ) \
+  Y(TERMINATE, exit(n0))
+
+#define REQUIRED_SERIAL_SUPPORT \
+  X("Serial.begin", SERIAL_BEGIN, DROP) \
+  X("Serial.end", SERIAL_END, ) \
+  X("Serial.available", SERIAL_AVAILABLE, PUSH -1) \
+  X("Serial.readBytes", SERIAL_READ_BYTES, n0 = read(0, b1, n0); NIP) \
+  X("Serial.write", SERIAL_WRITE, n0 = write(1, b1, n0); NIP) \
+  X("Serial.flush", SERIAL_FLUSH, )
+
 #include "gen/esp32_sim_opcodes.h"
 #include "common/core.h"
 #include "common/interp.h"