diff --git a/app/user/wrap_printf.s b/app/user/wrap_printf.s
index 026ac452..3344056f 100644
--- a/app/user/wrap_printf.s
+++ b/app/user/wrap_printf.s
@@ -44,7 +44,13 @@
 .align 4
 .literal_position
 __wrap_printf:
-  addi a1, a1, -48      /* get some stack space                               */
+  movi a9, os_printf_enabled  /* a9 is caller saved                           */
+  l8ui a9, a9, 0              /* load os_printf_enabled flag                  */
+  bnez a9, 1f                 /* if it's enabled, we print everything         */
+  movi a9, _irom0_sdktext_end /* else we check if it's SDK called             */
+  bgeu a0, a9, 1f             /* ...and only print from user code             */
+  ret
+1:addi a1, a1, -48      /* get some stack space                               */
   s32i a0, a1,  0       /* store a0 at the bottom                             */
   s32i a2, a1, 16       /* copy the formatting string and first few arguments */
   s32i a3, a1, 20       /* ...onto the stack in a way that we get a struct    */
@@ -61,3 +67,9 @@ __wrap_printf:
   l32i a0, a1, 0        /* restore return address into a0                     */
   addi a1, a1, 48       /* release the stack                                  */
   ret                   /* all done                                           */
+
+/* Flag for controlling whether SDK printf()s are suppressed or not.
+ * This is to provide an RTOS-safe reimplementation of system_set_os_print(). */
+.section ".data"
+.globl os_printf_enabled
+os_printf_enabled: .byte 1
diff --git a/ld/nodemcu.ld b/ld/nodemcu.ld
index 7e832b36..f338ed64 100644
--- a/ld/nodemcu.ld
+++ b/ld/nodemcu.ld
@@ -91,6 +91,12 @@ SECTIONS
   .irom0.text : ALIGN(0x1000)
   {
     _irom0_text_start = ABSOLUTE(.);
+
+    /* To be able to suppress SDK printfs, we place all SDK code first, with
+     * a marker at the end that we can easily compare against. */
+    */rtos-sdk/lib/lib*.a:*.o(.irom*)
+    _irom0_sdktext_end = ABSOLUTE(.);
+
     *(.servercert.flash)
     *(.clientcert.flash)
     *(.irom0.literal .irom.literal .irom.text.literal .irom0.text .irom.text)
@@ -108,10 +114,6 @@ SECTIONS
     KEEP(*(.lua_rotable))
     LONG(0) LONG(0) /* Null-terminate the array */
 
-    /* SDK doesn't use libc functions, and are therefore safe to put in flash */
-    */libc.a:*.o(.text* .literal*)
-    /* end libc functions */
-
     _irom0_text_end = ABSOLUTE(.);
     _flash_used_end = ABSOLUTE(.);
   } >irom0_0_seg :irom0_0_phdr =0xffffffff
diff --git a/sdk-overrides/include/user_interface.h b/sdk-overrides/include/user_interface.h
index e195e1c9..09a1078f 100644
--- a/sdk-overrides/include/user_interface.h
+++ b/sdk-overrides/include/user_interface.h
@@ -3,7 +3,6 @@
 
 #define ets_timer_arm_new(tmr, ms, rpt, isms) os_timer_arm(tmr,ms,rpt)
 
-//#include_next "user_interface.h"
 #include "espressif/esp_system.h"
 #include "espressif/esp_misc.h"
 #include "espressif/esp_wifi.h"
@@ -11,9 +10,10 @@
 #include "espressif/esp_softap.h"
 #include "espressif/esp_timer.h"
 
-
-// FIXME
-static inline void system_set_os_print(uint8 onoff) { (void)onoff; }
+static inline void system_set_os_print(uint8_t onoff) {
+  extern uint8_t os_printf_enabled;
+  os_printf_enabled = onoff;
+}
 
 bool wifi_softap_deauth(uint8 mac[6]);