diff --git a/cpu/at91sam7s/Makefile.at91sam7s b/cpu/at91sam7s/Makefile.at91sam7s
index e5fe22fb2..ac53aa999 100644
--- a/cpu/at91sam7s/Makefile.at91sam7s
+++ b/cpu/at91sam7s/Makefile.at91sam7s
@@ -62,7 +62,7 @@ CFLAGSNO = -I. -I$(CONTIKI)/core -I$(CONTIKI_CPU) -I$(CONTIKI_CPU)/loader \
            -I$(CONTIKI)/platform/$(TARGET) \
            ${addprefix -I,$(APPDIRS)} \
            -DWITH_UIP -DWITH_ASCII -DMCK=$(MCK) \
-           -Wall $(ARCH_FLAGS) -g 
+           -Wall -Werror $(ARCH_FLAGS) -g 
 
 CFLAGS  += $(CFLAGSNO) -O -DRUN_AS_SYSTEM -DROM_RUN
 LDFLAGS += -T $(LINKERSCRIPT) -nostartfiles
@@ -145,7 +145,7 @@ ifdef CORE
 	$(CC) $(LDFLAGS) $(CFLAGS) -nostartfiles -o $@ $(filter-out %.a,$^) $(filter %.a,$^) -lc $(filter %.a,$^)
 
 symbols.c: $(CORE)
-	$(NM) $< | awk -f ../../tools/mknmlist > symbols.c
+	$(NM) $< | awk -f $(CONTIKI_CPU)/builtins.awk -f ../../tools/mknmlist > symbols.c
 
 else
 %.$(TARGET): %-nosyms.$(TARGET)
diff --git a/cpu/at91sam7s/builtins.awk b/cpu/at91sam7s/builtins.awk
new file mode 100644
index 000000000..367014e38
--- /dev/null
+++ b/cpu/at91sam7s/builtins.awk
@@ -0,0 +1,4 @@
+BEGIN {
+  builtin["_exit"] =	"void _exit()";
+  builtin["strlen"] =	"unsigned long strlen()";
+}
diff --git a/cpu/at91sam7s/newlib-syscalls.c b/cpu/at91sam7s/newlib-syscalls.c
index fdb40222e..b765cbb38 100644
--- a/cpu/at91sam7s/newlib-syscalls.c
+++ b/cpu/at91sam7s/newlib-syscalls.c
@@ -1,6 +1,7 @@
 #include <debug-uart.h>
 #include <sys/stat.h>
 #include <errno.h>
+#include <stdio.h>
 
 int
 _open(const char *name, int flags, int mode) {
@@ -74,7 +75,7 @@ _sbrk(int incr)
   prev_heap_end = heap_end;
   if (heap_end + incr > &__heap_end__) {
     printf("Heap full (requested %d, available %d)\n",
-	    incr, &__heap_end__ - heap_end);
+	    incr, (int)(&__heap_end__ - heap_end));
     errno = ENOMEM;
     return (caddr_t)-1;
   }
diff --git a/cpu/at91sam7s/rtimer-arch.h b/cpu/at91sam7s/rtimer-arch.h
index b4edcf0ca..e096a3a89 100644
--- a/cpu/at91sam7s/rtimer-arch.h
+++ b/cpu/at91sam7s/rtimer-arch.h
@@ -17,5 +17,6 @@
 
 void rtimer_arch_set(rtimer_clock_t t);
 
+rtimer_clock_t rtimer_arch_now(void);
 
 #endif /* __RTIMER_ARCH_H__ */