diff --git a/dlls/mssign32/mssign32.spec b/dlls/mssign32/mssign32.spec
index 07d7a996fdb..c7b3cef4662 100644
--- a/dlls/mssign32/mssign32.spec
+++ b/dlls/mssign32/mssign32.spec
@@ -24,7 +24,7 @@
 @ stub SignerCreateTimeStampRequest
 @ stub SignerFreeSignerContext
 @ stub SignerSign
-@ stub SignerSignEx
+@ stdcall SignerSignEx(long ptr ptr ptr ptr wstr ptr ptr ptr)
 @ stub SignerTimeStamp
 @ stub SignerTimeStampEx
 @ stub SpcGetCertFromKey
diff --git a/dlls/mssign32/mssign32_main.c b/dlls/mssign32/mssign32_main.c
index e35488bad3e..2a5365e028d 100644
--- a/dlls/mssign32/mssign32_main.c
+++ b/dlls/mssign32/mssign32_main.c
@@ -28,6 +28,8 @@
 
 #include "wine/debug.h"
 
+#include "mssign32_private.h"
+
 WINE_DEFAULT_DEBUG_CHANNEL(mssign);
 
 BOOL WINAPI DllMain( HINSTANCE hinst, DWORD reason, LPVOID lpv )
@@ -72,3 +74,13 @@ void WINAPI PvkFreeCryptProv(HCRYPTPROV hProv, LPCWSTR pwszCapiProvider, DWORD d
     FIXME("%08lx %s %d %s stub\n", hProv, debugstr_w(pwszCapiProvider), dwProviderType,
                     debugstr_w(pwszTmpContainer));
 }
+
+HRESULT WINAPI SignerSignEx(DWORD flags, SIGNER_SUBJECT_INFO *subject_info, SIGNER_CERT *signer_cert,
+                            SIGNER_SIGNATURE_INFO *signature_info, SIGNER_PROVIDER_INFO *provider_info,
+                            const WCHAR *http_time_stamp, CRYPT_ATTRIBUTES *request, void *sip_data,
+                            SIGNER_CONTEXT **signer_context)
+{
+    FIXME("%x %p %p %p %p %s %p %p %p stub\n", flags, subject_info, signer_cert, signature_info, provider_info,
+                    wine_dbgstr_w(http_time_stamp), request, sip_data, signer_cert);
+    return E_NOTIMPL;
+}
diff --git a/dlls/mssign32/mssign32_private.h b/dlls/mssign32/mssign32_private.h
new file mode 100644
index 00000000000..a4e5d360a75
--- /dev/null
+++ b/dlls/mssign32/mssign32_private.h
@@ -0,0 +1,124 @@
+/*
+ * Copyright 2019 Gijs Vermeulen
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
+ */
+
+#include "windef.h"
+#include "winbase.h"
+#include "wincrypt.h"
+
+#define SPC_EXC_PE_PAGE_HASHES_FLAG         0x10
+#define SPC_INC_PE_IMPORT_ADDR_TABLE_FLAG   0x20
+#define SPC_INC_PE_DEBUG_INFO_FLAG          0x40
+#define SPC_INC_PE_RESOURCES_FLAG           0x80
+#define SPC_INC_PE_PAGE_HASHES_FLAG         0x100
+
+#define SIGNER_CERT_SPC_FILE    1
+#define SIGNER_CERT_STORE       2
+#define SIGNER_CERT_SPC_CHAIN   3
+
+#define SIGNER_CERT_POLICY_STORE            0x1
+#define SIGNER_CERT_POLICY_CHAIN            0x2
+#define SIGNER_CERT_POLICY_CHAIN_NO_ROOT    0x8
+
+#define SIGNER_NO_ATTR          0
+#define SIGNER_AUTHCODE_ATTR    1
+
+typedef struct _SIGNER_CONTEXT {
+    DWORD cbSize;
+    DWORD cbBlob;
+    BYTE  *pbBlob;
+} SIGNER_CONTEXT, *PSIGNER_CONTEXT;
+
+typedef struct _SIGNER_FILE_INFO {
+    DWORD       cbSize;
+    const WCHAR *pwszFileName;
+    HANDLE      hFile;
+} SIGNER_FILE_INFO, *PSIGNER_FILE_INFO;
+
+typedef struct _SIGNER_BLOB_INFO {
+    DWORD       cbSize;
+    GUID        *pGuidSubject;
+    DWORD       cbBlob;
+    BYTE        *pbBlob;
+    const WCHAR *pwszDisplayName;
+} SIGNER_BLOB_INFO, *PSIGNER_BLOB_INFO;
+
+typedef struct _SIGNER_SUBJECT_INFO {
+    DWORD cbSize;
+    DWORD *pdwIndex;
+    DWORD dwSubjectChoice;
+    union {
+        SIGNER_FILE_INFO *pSignerFileInfo;
+        SIGNER_BLOB_INFO *pSignerBlobInfo;
+    };
+} SIGNER_SUBJECT_INFO, *PSIGNER_SUBJECT_INFO;
+
+typedef struct _SIGNER_CERT_STORE_INFO {
+    DWORD              cbSize;
+    const CERT_CONTEXT *pSigningCert;
+    DWORD              dwCertPolicy;
+    HCERTSTORE         hCertStore;
+} SIGNER_CERT_STORE_INFO, *PSIGNER_CERT_STORE_INFO;
+
+typedef struct _SIGNER_SPC_CHAIN_INFO {
+    DWORD       cbSize;
+    const WCHAR *pwszSpcFile;
+    DWORD       dwCertPolicy;
+    HCERTSTORE  hCertStore;
+} SIGNER_SPC_CHAIN_INFO, *PSIGNER_SPC_CHAIN_INFO;
+
+typedef struct _SIGNER_CERT {
+    DWORD cbSize;
+    DWORD dwCertChoice;
+    union {
+        const WCHAR            *pwszSpcFile;
+        SIGNER_CERT_STORE_INFO *pCertStoreInfo;
+        SIGNER_SPC_CHAIN_INFO  *pSpcChainInfo;
+    };
+    HWND  hwnd;
+} SIGNER_CERT, *PSIGNER_CERT;
+
+typedef struct _SIGNER_ATTR_AUTHCODE {
+    DWORD       cbSize;
+    BOOL        fCommercial;
+    BOOL        fIndividual;
+    const WCHAR *pwszName;
+    const WCHAR *pwszInfo;
+} SIGNER_ATTR_AUTHCODE, *PSIGNER_ATTR_AUTHCODE;
+
+typedef struct _SIGNER_SIGNATURE_INFO {
+    DWORD            cbSize;
+    ALG_ID           algidHash;
+    DWORD            dwAttrChoice;
+    union {
+        SIGNER_ATTR_AUTHCODE *pAttrAuthcode;
+    };
+    CRYPT_ATTRIBUTES *psAuthenticated;
+    CRYPT_ATTRIBUTES *psUnauthenticated;
+} SIGNER_SIGNATURE_INFO, *PSIGNER_SIGNATURE_INFO;
+
+typedef struct _SIGNER_PROVIDER_INFO {
+    DWORD       cbSize;
+    const WCHAR *pwszProviderName;
+    DWORD       dwProviderType;
+    DWORD       dwKeySpec;
+    DWORD       dwPvkChoice;
+    union {
+        WCHAR *pwszPvkFileName;
+        WCHAR *pwszKeyContainer;
+    };
+} SIGNER_PROVIDER_INFO, *PSIGNER_PROVIDER_INFO;