diff --git a/cfg/avr.cfg b/cfg/avr.cfg
index dba601157..609ed7870 100644
--- a/cfg/avr.cfg
+++ b/cfg/avr.cfg
@@ -272,5 +272,21 @@
   <define name="RANDOM_MAX" value="0x7FFFFFFF"/>
   <define name="DTOSTR_ALWAYS_SIGN" value="0x01"/>
   <define name="DTOSTR_PLUS_SIGN" value="0x02"/>
-  <define name="DTOSTR_UPPERCASE" value="0x04"/>   
+  <define name="DTOSTR_UPPERCASE" value="0x04"/>
+  <!-- string.h -->
+  <function name="ffs">
+	  <noreturn>false</noreturn>
+	  <leak-ignore/>
+	  <arg nr="1"><not-uninit/></arg>
+  </function>
+  <function name="ffsl">
+	  <noreturn>false</noreturn>
+	  <leak-ignore/>
+	  <arg nr="1"><not-uninit/></arg>
+  </function>
+  <function name="ffsll">
+	  <noreturn>false</noreturn>
+	  <leak-ignore/>
+	  <arg nr="1"><not-uninit/></arg>
+  </function>     
 </def>