diff --git a/arch/arm/boot/compressed/decompress.c b/arch/arm/boot/compressed/decompress.c
index a0765e7ed6c7..ea7832702a8f 100644
--- a/arch/arm/boot/compressed/decompress.c
+++ b/arch/arm/boot/compressed/decompress.c
@@ -32,6 +32,7 @@ extern void error(char *);
 
 /* Not needed, but used in some headers pulled in by decompressors */
 extern char * strstr(const char * s1, const char *s2);
+extern size_t strlen(const char *s);
 
 #ifdef CONFIG_KERNEL_GZIP
 #include "../../../../lib/decompress_inflate.c"