diff --git a/board/drivers/dac.h b/board/drivers/dac.h
index 239f0fa79db276..ac565eb221cd05 100644
--- a/board/drivers/dac.h
+++ b/board/drivers/dac.h
@@ -1,3 +1,6 @@
+void puth(unsigned int i);
+void puts(const char *a);
+
 void dac_init(void) {
   // no buffers required since we have an opamp
   //DAC->CR = DAC_CR_EN1 | DAC_CR_BOFF1 | DAC_CR_EN2 | DAC_CR_BOFF2;
@@ -11,6 +14,10 @@ void dac_set(int channel, uint32_t value) {
     DAC->DHR12R1 = value;
   } else if (channel == 1) {
     DAC->DHR12R2 = value;
+  } else {
+    puts("Failed to set DAC: invalid channel value: ");
+    puth(value);
+    puts("\n");
   }
 }
 
diff --git a/board/drivers/uart.h b/board/drivers/uart.h
index 351e1f95114e34..5c5452483d0479 100644
--- a/board/drivers/uart.h
+++ b/board/drivers/uart.h
@@ -304,7 +304,8 @@ void putch(const char a) {
 
     //putc(&debug_ring, a);
   } else {
-    injectc(&debug_ring, a);
+    // misra-c2012-17.7: serial debug function, ok to ignore output
+    (void)injectc(&debug_ring, a);
   }
 }