diff --git a/gnucash.modules b/gnucash.modules
index eb5a838e..aebcddf3 100644
--- a/gnucash.modules
+++ b/gnucash.modules
@@ -146,6 +146,7 @@
   <autotools id="gwenhywfar" autogen-sh="configure"
 	     autogenargs="--with-guis='gtk3' --enable-local-install --disable-binreloc --disable-ssl">
     <branch module="download.php?package=01&amp;release=208&amp;file=02&amp;dummy=gwenhywfar-4.20.0.tar.gz" version="4.20.0" repo="aqbanking" checkoutdir="gwenhywfar-4.20.0">
+            <patch file="https://raw.githubusercontent.com/Gnucash/gnucash-on-windows/master/patches/Fix-signature-mismatch-in-abgui.c.patch" strip='1'/>
     </branch>
     <dependencies>
       <dep package="gcrypt"/>
diff --git a/patches/Fix-signature-mismatch-in-abgui.c.patch b/patches/Fix-signature-mismatch-in-abgui.c.patch
new file mode 100644
index 00000000..78f33916
--- /dev/null
+++ b/patches/Fix-signature-mismatch-in-abgui.c.patch
@@ -0,0 +1,44 @@
+From d3870968869c022b4af18f45198d2a6d2296fac9 Mon Sep 17 00:00:00 2001
+From: John Ralls <jralls@ceridwen.us>
+Date: Sun, 25 Mar 2018 14:45:55 -0700
+Subject: [PATCH] Fix signature mismatch in abgui.c.
+
+---
+ src/libs/aqbanking/gui/abgui.c | 14 +++++++-------
+ 1 file changed, 7 insertions(+), 7 deletions(-)
+
+diff --git a/src/libs/aqbanking/gui/abgui.c b/src/libs/aqbanking/gui/abgui.c
+index f4a4407..aa51cb2 100644
+--- a/src/libs/aqbanking/gui/abgui.c
++++ b/src/libs/aqbanking/gui/abgui.c
+@@ -238,10 +238,10 @@ int AB_Gui_CheckCert(GWEN_GUI *gui,
+ 
+ 
+ 
+-int AB_Gui_ReadDialogPrefs(GWEN_GUI *gui,
+-			   const char *groupName,
+-			   const char *altName,
+-			   GWEN_DB_NODE **pDb) {
++int GWENHYWFAR_CB AB_Gui_ReadDialogPrefs(GWEN_GUI *gui,
++                                         const char *groupName,
++                                         const char *altName,
++                                         GWEN_DB_NODE **pDb) {
+   AB_GUI *xgui;
+ 
+   assert(gui);
+@@ -282,9 +282,9 @@ int AB_Gui_ReadDialogPrefs(GWEN_GUI *gui,
+ 
+ 
+ 
+-int AB_Gui_WriteDialogPrefs(GWEN_GUI *gui,
+-			    const char *groupName,
+-			    GWEN_DB_NODE *db) {
++int GWENHYWFAR_CB AB_Gui_WriteDialogPrefs(GWEN_GUI *gui,
++                                          const char *groupName,
++                                          GWEN_DB_NODE *db) {
+   AB_GUI *xgui;
+ 
+   assert(gui);
+-- 
+2.2.2
+