diff --git a/sys/include/systm.h b/sys/include/systm.h
index 5967000..94cbc76 100644
--- a/sys/include/systm.h
+++ b/sys/include/systm.h
@@ -70,6 +70,7 @@ extern dev_t    pipedev;            /* pipe device */
 
 extern  const char icode[];         /* user init code */
 extern  const char icodeend[];      /* its end */
+extern  const char initflags[];     /* init flags string */
 
 struct inode;
 daddr_t bmap (struct inode *ip, daddr_t bn, int rwflg, int flags);
diff --git a/sys/kernel/init_main.c b/sys/kernel/init_main.c
index 508813f..37e5045 100644
--- a/sys/kernel/init_main.c
+++ b/sys/kernel/init_main.c
@@ -196,6 +196,7 @@ main()
          * No return from sched. */
         sched();
     }
+
     /* Child process with pid 1: init. */
     s = splhigh();
     p = u.u_procp;
@@ -204,6 +205,15 @@ main()
     p->p_ssize = 1024;              /* one kbyte of stack */
     p->p_saddr = USER_DATA_END - 1024;
     bcopy ((caddr_t) icode, (caddr_t) USER_DATA_START, icodeend - icode);
+
+    /* Start in single user more, if asked. */
+    if (boothowto & RB_SINGLE) {
+        char *iflags = (char*) USER_DATA_START + (initflags - icode);
+
+        /* Call /sbin/init with option '-s'. */
+        iflags[1] = 's';
+    }
+
     /*
      * return goes to location 0 of user init code
      * just copied out.
diff --git a/sys/pic32/fubarino/Config b/sys/pic32/fubarino/Config
index d1f9690..6b8231e 100644
--- a/sys/pic32/fubarino/Config
+++ b/sys/pic32/fubarino/Config
@@ -26,6 +26,10 @@ options         "BUS_DIV=1"                 # Bus clock divisor 1/2/4/8
 # LED
 signal          "LED_KERNEL"    pin RE5     # kernel activity indicator
 
+# Button
+# Hold this button pressed at startup to enter single-user mode.
+signal          "BUTTON1"   pin RE7 invert  # PRG button, active low
+
 # Root filesystem at /dev/sd0a, swap at /dev/sd0b
 config          unix    root on sd0a
                         swap on sd0b
diff --git a/sys/pic32/fubarino/Makefile b/sys/pic32/fubarino/Makefile
index 1c87d5a..a35bd27 100644
--- a/sys/pic32/fubarino/Makefile
+++ b/sys/pic32/fubarino/Makefile
@@ -13,6 +13,7 @@ PARAM += -DGPIO5_ENABLED
 PARAM += -DGPIO6_ENABLED
 PARAM += -DADC_ENABLED
 PARAM += -DPWM_ENABLED
+PARAM += -DBUTTON1_PORT=TRISE -DBUTTON1_PIN=7 -DBUTTON1_INVERT
 PARAM += -DLED_KERNEL_PORT=TRISE -DLED_KERNEL_PIN=5
 PARAM += -DUSB_NUM_STRING_DESCRIPTORS=3
 PARAM += -DUSB_MAX_EP_NUMBER=3
diff --git a/sys/pic32/machdep.c b/sys/pic32/machdep.c
index 6cfa1c5..599885c 100644
--- a/sys/pic32/machdep.c
+++ b/sys/pic32/machdep.c
@@ -166,6 +166,26 @@ dev_t   dumpdev = NODEV;
 dev_t   pipedev;
 daddr_t dumplo = (daddr_t) 1024;
 
+/*
+ * Check whether button 1 is pressed.
+ */
+static inline int
+button1_pressed()
+{
+#ifdef BUTTON1_PORT
+    int val;
+
+    TRIS_SET(BUTTON1_PORT) = 1 << BUTTON1_PIN;
+    val = PORT_VAL(BUTTON1_PORT);
+#ifdef BUTTON1_INVERT
+    val = ~val;
+#endif
+    return (val >> BUTTON1_PIN) & 1;
+#else
+    return 0;
+#endif
+}
+
 /*
  * Machine dependent startup code
  */
@@ -391,6 +411,14 @@ startup()
 
     /* Get total RAM size. */
     physmem = BMXDRMSZ;
+
+    /*
+     * When button 1 is pressed - boot to single user mode.
+     */
+    boothowto = 0;
+    if (button1_pressed()) {
+        boothowto |= RB_SINGLE;
+    }
 }
 
 static void cpuidentify()
diff --git a/sys/pic32/startup.S b/sys/pic32/startup.S
index fcbe9b2..9bb3b85 100644
--- a/sys/pic32/startup.S
+++ b/sys/pic32/startup.S
@@ -310,9 +310,11 @@ single_step_done:
 # Icode is copied out to process 1 to exec /sbin/init.
 # If the exec fails, process 1 exits.
 #
-                .globl  icode, icodeend
+                .globl  icode, icodeend, initflags
                 .type   icode, @function
                 .type   icodeend, @function
+                .type   etcinit, @object
+                .type   argv, @object
 icode:
                 la      $a0, UBASE
                 move    $a1, $a0
@@ -323,8 +325,9 @@ icode:
                 syscall 1                               # SYS_exit
 etcinit:
                 .ascii  "/sbin/init\0"
+                .align  2
 initflags:
-                .ascii  "-\0"                           # ASCII initflags
+                .ascii  "-\0\0\0\0\0\0\0\0\0\0"         # space for options
 argv:
                 .word   etcinit + 6 - icode + UBASE     # address of "init\0"
                 .word   initflags - icode + UBASE       # init options