diff --git a/marshal.h b/marshal.h
index 817620ea..bc020a8d 100644
--- a/marshal.h
+++ b/marshal.h
@@ -282,6 +282,8 @@ static inline void BinarySource_INIT__(BinarySource *src, ptrlen data)
     BinarySource_get_rsa_ssh1_pub(BinarySource_UPCAST(src), rsa, order)
 #define get_rsa_ssh1_priv(src, rsa) \
     BinarySource_get_rsa_ssh1_priv(BinarySource_UPCAST(src), rsa)
+#define get_rsa_ssh1_priv_agent(src) \
+    BinarySource_get_rsa_ssh1_priv_agent(BinarySource_UPCAST(src))
 
 #define get_err(src) (BinarySource_UPCAST(src)->err)
 #define get_avail(src) (BinarySource_UPCAST(src)->len - \
diff --git a/pageant.c b/pageant.c
index c5cef934..70b21743 100644
--- a/pageant.c
+++ b/pageant.c
@@ -379,19 +379,7 @@ void pageant_handle_msg(BinarySink *bs,
 
             plog(logctx, logfn, "request: SSH1_AGENTC_ADD_RSA_IDENTITY");
 
-            key = snew(RSAKey);
-            memset(key, 0, sizeof(RSAKey));
-
-            get_rsa_ssh1_pub(msg, key, RSA_SSH1_MODULUS_FIRST);
-            get_rsa_ssh1_priv(msg, key);
-
-            /* SSH-1 names p and q the other way round, i.e. we have
-             * the inverse of p mod q and not of q mod p. We swap the
-             * names, because our internal RSA wants iqmp. */
-            key->iqmp = get_mp_ssh1(msg);
-            key->q = get_mp_ssh1(msg);
-            key->p = get_mp_ssh1(msg);
-
+            key = get_rsa_ssh1_priv_agent(msg);
             key->comment = mkstr(get_string(msg));
 
             if (get_err(msg)) {
diff --git a/ssh.h b/ssh.h
index 06725247..af0f9d47 100644
--- a/ssh.h
+++ b/ssh.h
@@ -539,6 +539,7 @@ void BinarySource_get_rsa_ssh1_pub(
     BinarySource *src, RSAKey *result, RsaSsh1Order order);
 void BinarySource_get_rsa_ssh1_priv(
     BinarySource *src, RSAKey *rsa);
+RSAKey *BinarySource_get_rsa_ssh1_priv_agent(BinarySource *src);
 bool rsa_ssh1_encrypt(unsigned char *data, int length, RSAKey *key);
 mp_int *rsa_ssh1_decrypt(mp_int *input, RSAKey *key);
 bool rsa_ssh1_decrypt_pkcs1(mp_int *input, RSAKey *key, strbuf *outbuf);
diff --git a/sshrsa.c b/sshrsa.c
index e30ca474..4b7f4b5d 100644
--- a/sshrsa.c
+++ b/sshrsa.c
@@ -43,6 +43,24 @@ void BinarySource_get_rsa_ssh1_priv(
     rsa->private_exponent = get_mp_ssh1(src);
 }
 
+RSAKey *BinarySource_get_rsa_ssh1_priv_agent(BinarySource *src)
+{
+    RSAKey *rsa = snew(RSAKey);
+    memset(rsa, 0, sizeof(RSAKey));
+
+    get_rsa_ssh1_pub(src, rsa, RSA_SSH1_MODULUS_FIRST);
+    get_rsa_ssh1_priv(src, rsa);
+
+    /* SSH-1 names p and q the other way round, i.e. we have the
+     * inverse of p mod q and not of q mod p. We swap the names,
+     * because our internal RSA wants iqmp. */
+    rsa->iqmp = get_mp_ssh1(src);
+    rsa->q = get_mp_ssh1(src);
+    rsa->p = get_mp_ssh1(src);
+
+    return rsa;
+}
+
 bool rsa_ssh1_encrypt(unsigned char *data, int length, RSAKey *key)
 {
     mp_int *b1, *b2;
diff --git a/testcrypt.h b/testcrypt.h
index 5f1fd612..7dc49cb8 100644
--- a/testcrypt.h
+++ b/testcrypt.h
@@ -187,12 +187,15 @@ FUNC2(void, ssh_ecdhkex_getpublic, val_ecdh, out_val_string_binarysink)
 FUNC2(val_mpint, ssh_ecdhkex_getkey, val_ecdh, val_string_ptrlen)
 
 /*
- * RSA key exchange.
+ * RSA key exchange, and also the BinarySource get function
+ * get_ssh1_rsa_priv_agent, which is a convenient way to make an
+ * RSAKey for RSA kex testing purposes.
  */
 FUNC1(val_rsakex, ssh_rsakex_newkey, val_string_ptrlen)
 FUNC1(uint, ssh_rsakex_klen, val_rsakex)
 FUNC3(val_string, ssh_rsakex_encrypt, val_rsakex, hashalg, val_string_ptrlen)
 FUNC3(val_mpint, ssh_rsakex_decrypt, val_rsakex, hashalg, val_string_ptrlen)
+FUNC1(val_rsakex, get_rsa_ssh1_priv_agent, val_string_binarysource)
 
 /*
  * Bare RSA keys as used in SSH-1. The construction API functions