diff --git a/doc/configuration.txt b/doc/configuration.txt
index c1f6f82..dd8d588 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -15150,6 +15150,13 @@
   microseconds since epoch. Offset is assumed to have the same unit as
   input timestamp.
 
+iif(<true>,<false>)
+  Returns the <true> string if the input value is true. Returns the <false>
+  string otherwise.
+
+  Example:
+    http-request set-header x-forwarded-proto %[ssl_fc,iff(https,http)]
+
 in_table(<table>)
   Uses the string representation of the input sample to perform a look up in
   the specified table. If the key is not found in the table, a boolean false
diff --git a/reg-tests/converter/iif.vtc b/reg-tests/converter/iif.vtc
new file mode 100644
index 0000000..360b63f
--- /dev/null
+++ b/reg-tests/converter/iif.vtc
@@ -0,0 +1,45 @@
+varnishtest "iif converter Test"
+
+feature ignore_unknown_macro
+
+server s1 {
+	rxreq
+	txresp
+} -repeat 3 -start
+
+haproxy h1 -conf {
+    defaults
+	mode http
+	timeout connect 1s
+	timeout client  1s
+	timeout server  1s
+
+    frontend fe
+	bind "fd@${fe}"
+
+	#### requests
+	http-request set-var(txn.iif) req.hdr_cnt(count),iif(ok,ko)
+	http-response set-header iif %[var(txn.iif)]
+
+	default_backend be
+
+    backend be
+	server s1 ${s1_addr}:${s1_port}
+} -start
+
+client c1 -connect ${h1_fe_sock} {
+	txreq
+	rxresp
+	expect resp.status == 200
+	expect resp.http.iif == "ko"
+	txreq \
+		-hdr "count: 1"
+	rxresp
+	expect resp.status == 200
+	expect resp.http.iif == "ok"
+	txreq \
+		-hdr "count: 1,2"
+	rxresp
+	expect resp.status == 200
+	expect resp.http.iif == "ok"
+} -run
diff --git a/src/sample.c b/src/sample.c
index 3a15348..a9c08ef 100644
--- a/src/sample.c
+++ b/src/sample.c
@@ -3121,6 +3121,26 @@
 }
 #endif
 
+/* Takes a boolean as input. Returns the first argument if that boolean is true and
+ * the second argument otherwise.
+ */
+static int sample_conv_iif(const struct arg *arg_p, struct sample *smp, void *private)
+{
+	smp->data.type = SMP_T_STR;
+	smp->flags |= SMP_F_CONST;
+
+	if (smp->data.u.sint) {
+		smp->data.u.str.data = arg_p[0].data.str.data;
+		smp->data.u.str.area = arg_p[0].data.str.area;
+	}
+	else {
+		smp->data.u.str.data = arg_p[1].data.str.data;
+		smp->data.u.str.area = arg_p[1].data.str.area;
+	}
+
+	return 1;
+}
+
 #define GRPC_MSG_COMPRESS_FLAG_SZ 1 /* 1 byte */
 #define GRPC_MSG_LENGTH_SZ        4 /* 4 bytes */
 #define GRPC_MSG_HEADER_SZ        (GRPC_MSG_COMPRESS_FLAG_SZ + GRPC_MSG_LENGTH_SZ)
@@ -3782,6 +3802,8 @@
 	{ "ungrpc", sample_conv_ungrpc,    ARG2(1,PBUF_FNUM,STR), sample_conv_protobuf_check, SMP_T_BIN, SMP_T_BIN  },
 	{ "protobuf", sample_conv_protobuf, ARG2(1,PBUF_FNUM,STR), sample_conv_protobuf_check, SMP_T_BIN, SMP_T_BIN  },
 
+	{ "iif", sample_conv_iif, ARG2(2, STR, STR), NULL, SMP_T_BOOL, SMP_T_STR },
+
 	{ "and",    sample_conv_binary_and, ARG1(1,STR), check_operator, SMP_T_SINT, SMP_T_SINT  },
 	{ "or",     sample_conv_binary_or,  ARG1(1,STR), check_operator, SMP_T_SINT, SMP_T_SINT  },
 	{ "xor",    sample_conv_binary_xor, ARG1(1,STR), check_operator, SMP_T_SINT, SMP_T_SINT  },