diff --git a/dlls/wintrust/register.c b/dlls/wintrust/register.c
index 0a02ed209da..9b97d9cc511 100644
--- a/dlls/wintrust/register.c
+++ b/dlls/wintrust/register.c
@@ -837,7 +837,7 @@ BOOL WINAPI WintrustLoadFunctionPointers( GUID* pgActionID,
     pPfns->pfnAlloc = WINTRUST_Alloc;
     pPfns->pfnFree = WINTRUST_Free;
     pPfns->pfnAddStore2Chain = WINTRUST_AddStore;
-    pPfns->pfnAddSgnr2Chain = NULL;
+    pPfns->pfnAddSgnr2Chain = WINTRUST_AddSgnr;
     pPfns->pfnAddCert2Chain = NULL;
     pPfns->pfnAddPrivData2Chain = NULL;
     pPfns->psUIpfns = NULL;
diff --git a/dlls/wintrust/tests/softpub.c b/dlls/wintrust/tests/softpub.c
index 1eb967a72e4..b1ca23a9a84 100644
--- a/dlls/wintrust/tests/softpub.c
+++ b/dlls/wintrust/tests/softpub.c
@@ -91,6 +91,7 @@ static void test_utils(SAFE_PROVIDER_FUNCTIONS *funcs)
 {
     CRYPT_PROVIDER_DATA data = { 0 };
     HCERTSTORE store;
+    CRYPT_PROVIDER_SGNR sgnr = { 0 };
     BOOL ret;
 
     /* Crash
@@ -118,6 +119,44 @@ static void test_utils(SAFE_PROVIDER_FUNCTIONS *funcs)
     }
     else
         skip("CertOpenStore failed: %08x\n", GetLastError());
+
+    /* Crash
+    ret = funcs->pfnAddSgnr2Chain(NULL, FALSE, 0, NULL);
+    ret = funcs->pfnAddSgnr2Chain(&data, FALSE, 0, NULL);
+     */
+    ret = funcs->pfnAddSgnr2Chain(&data, FALSE, 0, &sgnr);
+    ok(ret, "pfnAddSgnr2Chain failed: %08x\n", GetLastError());
+    ok(data.csSigners == 1, "Expected 1 signer, got %d\n", data.csSigners);
+    ok(data.pasSigners != NULL, "Expected pasSigners to be allocated\n");
+    if (data.pasSigners)
+    {
+        ok(!memcmp(&data.pasSigners[0], &sgnr, sizeof(sgnr)),
+         "Unexpected data in signer\n");
+        /* Adds into the location specified by the index */
+        sgnr.cbStruct = sizeof(CRYPT_PROVIDER_SGNR);
+        sgnr.sftVerifyAsOf.dwLowDateTime = 0xdeadbeef;
+        ret = funcs->pfnAddSgnr2Chain(&data, FALSE, 1, &sgnr);
+        ok(ret, "pfnAddSgnr2Chain failed: %08x\n", GetLastError());
+        ok(data.csSigners == 2, "Expected 2 signers, got %d\n", data.csSigners);
+        ok(!memcmp(&data.pasSigners[1], &sgnr, sizeof(sgnr)),
+         "Unexpected data in signer\n");
+        /* This also adds, but the data aren't copied */
+        sgnr.cbStruct = sizeof(DWORD);
+        ret = funcs->pfnAddSgnr2Chain(&data, FALSE, 0, &sgnr);
+        ok(ret, "pfnAddSgnr2Chain failed: %08x\n", GetLastError());
+        ok(data.csSigners == 3, "Expected 3 signers, got %d\n", data.csSigners);
+        ok(data.pasSigners[0].cbStruct == 0, "Unexpected data size %d\n",
+         data.pasSigners[0].cbStruct);
+        ok(data.pasSigners[0].sftVerifyAsOf.dwLowDateTime == 0,
+         "Unexpected verify time %d\n",
+         data.pasSigners[0].sftVerifyAsOf.dwLowDateTime);
+        /* But too large a thing isn't added */
+        sgnr.cbStruct = sizeof(sgnr) + sizeof(DWORD);
+        SetLastError(0xdeadbeef);
+        ret = funcs->pfnAddSgnr2Chain(&data, FALSE, 0, &sgnr);
+        ok(!ret && GetLastError() == ERROR_INVALID_PARAMETER,
+         "Expected ERROR_INVALID_PARAMETER, got %d\n", GetLastError());
+    }
 }
 
 static void testInitialize(SAFE_PROVIDER_FUNCTIONS *funcs, GUID *actionID)
diff --git a/dlls/wintrust/wintrust_main.c b/dlls/wintrust/wintrust_main.c
index 6ecfb1daa2d..0f6dcd609de 100644
--- a/dlls/wintrust/wintrust_main.c
+++ b/dlls/wintrust/wintrust_main.c
@@ -252,3 +252,54 @@ BOOL WINAPI WINTRUST_AddStore(CRYPT_PROVIDER_DATA *data, HCERTSTORE store)
         SetLastError(ERROR_OUTOFMEMORY);
     return ret;
 }
+
+BOOL WINAPI WINTRUST_AddSgnr(CRYPT_PROVIDER_DATA *data,
+ BOOL fCounterSigner, DWORD idxSigner, CRYPT_PROVIDER_SGNR *sgnr)
+{
+    BOOL ret = FALSE;
+
+    if (sgnr->cbStruct > sizeof(CRYPT_PROVIDER_SGNR))
+    {
+        SetLastError(ERROR_INVALID_PARAMETER);
+        return FALSE;
+    }
+    if (fCounterSigner)
+    {
+        FIXME("unimplemented for counter signers\n");
+        SetLastError(ERROR_INVALID_PARAMETER);
+        return FALSE;
+    }
+    if (data->csSigners)
+        data->pasSigners = WINTRUST_ReAlloc(data->pasSigners,
+         (data->csSigners + 1) * sizeof(CRYPT_PROVIDER_SGNR));
+    else
+    {
+        data->pasSigners = WINTRUST_Alloc(sizeof(CRYPT_PROVIDER_SGNR));
+        data->csSigners = 0;
+    }
+    if (data->pasSigners)
+    {
+        if (idxSigner < data->csSigners)
+            memmove(&data->pasSigners[idxSigner],
+             &data->pasSigners[idxSigner + 1],
+             (data->csSigners - idxSigner) * sizeof(CRYPT_PROVIDER_SGNR));
+        ret = TRUE;
+        if (sgnr->cbStruct == sizeof(CRYPT_PROVIDER_SGNR))
+        {
+            /* The PSDK says psSigner should be allocated using pfnAlloc, but
+             * it doesn't say anything about ownership.  Since callers are
+             * internal, assume ownership is passed, and just store the
+             * pointer.
+             */
+            memcpy(&data->pasSigners[idxSigner], sgnr,
+             sizeof(CRYPT_PROVIDER_SGNR));
+        }
+        else
+            memset(&data->pasSigners[idxSigner], 0,
+             sizeof(CRYPT_PROVIDER_SGNR));
+        data->csSigners++;
+    }
+    else
+        SetLastError(ERROR_OUTOFMEMORY);
+    return ret;
+}
diff --git a/dlls/wintrust/wintrust_priv.h b/dlls/wintrust/wintrust_priv.h
index 40f2e5d9d1a..75b043845df 100644
--- a/dlls/wintrust/wintrust_priv.h
+++ b/dlls/wintrust/wintrust_priv.h
@@ -22,5 +22,7 @@ void * WINAPI WINTRUST_Alloc(DWORD cb);
 void * WINAPI WINTRUST_ReAlloc(void *ptr, DWORD cb);
 void WINAPI WINTRUST_Free(void *p);
 BOOL WINAPI WINTRUST_AddStore(CRYPT_PROVIDER_DATA *data, HCERTSTORE store);
+BOOL WINAPI WINTRUST_AddSgnr(CRYPT_PROVIDER_DATA *data,
+ BOOL fCounterSigner, DWORD idxSigner, CRYPT_PROVIDER_SGNR *sgnr);
 
 #endif /* ndef __WINTRUST_PRIV_H__ */