diff --git a/bootstrap.conf b/bootstrap.conf
index 6befd747..55a6e3ce 100644
--- a/bootstrap.conf
+++ b/bootstrap.conf
@@ -32,6 +32,7 @@ base32
 bind
 c-ctype
 c-strcase
+c-strcasestr
 clock-time
 close
 connect
diff --git a/src/iri.c b/src/iri.c
index 0686f301..f46ee078 100644
--- a/src/iri.c
+++ b/src/iri.c
@@ -40,6 +40,7 @@ as that of the covered work.  */
 #include "utils.h"
 #include "url.h"
 #include "c-strcase.h"
+#include "c-strcasestr.h"
 
 /* RFC3987 section 3.1 mandates STD3 ASCII RULES */
 #define IDNA_FLAGS  IDNA_USE_STD3_ASCII_RULES
@@ -56,7 +57,7 @@ parse_charset (char *str)
   if (!str || !*str)
     return NULL;
 
-  str = strcasestr (str, "charset=");
+  str = c_strcasestr (str, "charset=");
   if (!str)
     return NULL;