diff --git a/idzhook/config.c b/idzhook/config.c
index 2987584..c8d551d 100644
--- a/idzhook/config.c
+++ b/idzhook/config.c
@@ -8,10 +8,27 @@
 #include "board/sg-reader.h"
 
 #include "idzhook/config.h"
+#include "idzhook/idz-dll.h"
 
 #include "platform/config.h"
 #include "platform/platform.h"
 
+void idz_dll_config_load(
+        struct idz_dll_config *cfg,
+        const wchar_t *filename)
+{
+    assert(cfg != NULL);
+    assert(filename != NULL);
+
+    GetPrivateProfileStringW(
+            L"idzio",
+            L"path",
+            L"",
+            cfg->path,
+            _countof(cfg->path),
+            filename);
+}
+
 void idz_hook_config_load(
         struct idz_hook_config *cfg,
         const wchar_t *filename)
@@ -22,6 +39,7 @@ void idz_hook_config_load(
     platform_config_load(&cfg->platform, filename);
     amex_config_load(&cfg->amex, filename);
     aime_config_load(&cfg->aime, filename);
+    idz_dll_config_load(&cfg->dll, filename);
     zinput_config_load(&cfg->zinput, filename);
 }
 
diff --git a/idzhook/config.h b/idzhook/config.h
index a93cb11..a7cf964 100644
--- a/idzhook/config.h
+++ b/idzhook/config.h
@@ -7,6 +7,7 @@
 
 #include "board/sg-reader.h"
 
+#include "idzhook/idz-dll.h"
 #include "idzhook/zinput.h"
 
 #include "platform/platform.h"
@@ -15,9 +16,14 @@ struct idz_hook_config {
     struct platform_config platform;
     struct amex_config amex;
     struct aime_config aime;
+    struct idz_dll_config dll;
     struct zinput_config zinput;
 };
 
+void idz_dll_config_load(
+        struct idz_dll_config *cfg,
+        const wchar_t *filename);
+
 void idz_hook_config_load(
         struct idz_hook_config *cfg,
         const wchar_t *filename);
diff --git a/idzhook/dllmain.c b/idzhook/dllmain.c
index d1dd208..fd15f09 100644
--- a/idzhook/dllmain.c
+++ b/idzhook/dllmain.c
@@ -13,6 +13,7 @@
 #include "hooklib/spike.h"
 
 #include "idzhook/config.h"
+#include "idzhook/idz-dll.h"
 #include "idzhook/jvs.h"
 #include "idzhook/zinput.h"
 
@@ -51,6 +52,12 @@ static DWORD CALLBACK idz_pre_startup(void)
         goto fail;
     }
 
+    hr = idz_dll_init(&idz_hook_cfg.dll, idz_hook_mod);
+
+    if (FAILED(hr)) {
+        goto fail;
+    }
+
     hr = amex_hook_init(&idz_hook_cfg.amex, idz_jvs_init);
 
     if (FAILED(hr)) {
diff --git a/idzhook/idz-dll.c b/idzhook/idz-dll.c
new file mode 100644
index 0000000..2ebc75b
--- /dev/null
+++ b/idzhook/idz-dll.c
@@ -0,0 +1,112 @@
+#include <windows.h>
+
+#include <assert.h>
+#include <stdlib.h>
+
+#include "idzhook/idz-dll.h"
+
+#include "util/dll-bind.h"
+#include "util/dprintf.h"
+
+const struct dll_bind_sym idz_dll_syms[] = {
+    {
+        .sym = "idz_io_jvs_init",
+        .off = offsetof(struct idz_dll, jvs_init),
+    }, {
+        .sym = "idz_io_jvs_read_analogs",
+        .off = offsetof(struct idz_dll, jvs_read_analogs),
+    }, {
+        .sym = "idz_io_jvs_read_buttons",
+        .off = offsetof(struct idz_dll, jvs_read_buttons),
+    }, {
+        .sym = "idz_io_jvs_read_shifter",
+        .off = offsetof(struct idz_dll, jvs_read_shifter),
+    }, {
+        .sym = "idz_io_jvs_read_coin_counter",
+        .off = offsetof(struct idz_dll, jvs_read_coin_counter),
+    }
+};
+
+struct idz_dll idz_dll;
+
+// Copypasta DLL binding and diagnostic message boilerplate.
+// Not much of this lends itself to being easily factored out. Also there
+// will be a lot of API-specific branching code here eventually as new API
+// versions get defined, so even though these functions all look the same
+// now this won't remain the case forever.
+
+HRESULT idz_dll_init(const struct idz_dll_config *cfg, HINSTANCE self)
+{
+    uint16_t (*get_api_version)(void);
+    const struct dll_bind_sym *sym;
+    HINSTANCE owned;
+    HINSTANCE src;
+    HRESULT hr;
+
+    assert(cfg != NULL);
+    assert(self != NULL);
+
+    if (cfg->path[0] != L'\0') {
+        owned = LoadLibraryW(cfg->path);
+
+        if (owned == NULL) {
+            hr = HRESULT_FROM_WIN32(GetLastError());
+            dprintf("IDZ IO: Failed to load IO DLL: %x: %S\n",
+                    hr,
+                    cfg->path);
+
+            goto end;
+        }
+
+        dprintf("IDZ IO: Using custom IO DLL: %S\n", cfg->path);
+        src = owned;
+    } else {
+        owned = NULL;
+        src = self;
+    }
+
+    get_api_version = (void *) GetProcAddress(src, "idz_io_get_api_version");
+
+    if (get_api_version != NULL) {
+        idz_dll.api_version = get_api_version();
+    } else {
+        idz_dll.api_version = 0x0100;
+        dprintf("Custom IO DLL does not expose idz_io_get_api_version, "
+                "assuming API version 1.0.\n"
+                "Please ask the developer to update their DLL.\n");
+    }
+
+    if (idz_dll.api_version >= 0x0200) {
+        hr = E_NOTIMPL;
+        dprintf("IDZ IO: Custom IO DLL implements an unsupported "
+                "API version (%#04x). Please update Segatools.\n",
+                idz_dll.api_version);
+
+        goto end;
+    }
+
+    sym = idz_dll_syms;
+    hr = dll_bind(&idz_dll, src, &sym, _countof(idz_dll_syms));
+
+    if (FAILED(hr)) {
+        if (src != self) {
+            dprintf("IDZ IO: Custom IO DLL does not provide function "
+                    "\"%s\". Please contact your IO DLL's developer for "
+                    "further assistance.\n",
+                    sym->sym);
+
+            goto end;
+        } else {
+            dprintf("Internal error: could not reflect \"%s\"\n", sym->sym);
+        }
+    }
+
+    owned = NULL;
+
+end:
+    if (owned != NULL) {
+        FreeLibrary(owned);
+    }
+
+    return hr;
+}
diff --git a/idzhook/idz-dll.h b/idzhook/idz-dll.h
new file mode 100644
index 0000000..e67cb45
--- /dev/null
+++ b/idzhook/idz-dll.h
@@ -0,0 +1,22 @@
+#pragma once
+
+#include <windows.h>
+
+#include "idzio/idzio.h"
+
+struct idz_dll {
+    uint16_t api_version;
+    HRESULT (*jvs_init)(void);
+    void (*jvs_read_analogs)(struct idz_io_analog_state *out);
+    void (*jvs_read_buttons)(uint8_t *opbtn, uint8_t *gamebtn);
+    void (*jvs_read_shifter)(uint8_t *gear);
+    void (*jvs_read_coin_counter)(uint16_t *total);
+};
+
+struct idz_dll_config {
+    wchar_t path[MAX_PATH];
+};
+
+extern struct idz_dll idz_dll;
+
+HRESULT idz_dll_init(const struct idz_dll_config *cfg, HINSTANCE self);
diff --git a/idzhook/idzhook.def b/idzhook/idzhook.def
index 43b8ef7..a9b9f74 100644
--- a/idzhook/idzhook.def
+++ b/idzhook/idzhook.def
@@ -12,3 +12,8 @@ EXPORTS
     amDllVideoGetVBiosVersion @4
     amDllVideoOpen @1
     amDllVideoSetResolution @3
+    idz_io_jvs_init
+    idz_io_jvs_read_analogs
+    idz_io_jvs_read_buttons
+    idz_io_jvs_read_coin_counter
+    idz_io_jvs_read_shifter
diff --git a/idzhook/jvs.c b/idzhook/jvs.c
index fce5849..ab2f6aa 100644
--- a/idzhook/jvs.c
+++ b/idzhook/jvs.c
@@ -8,10 +8,9 @@
 
 #include "board/io3.h"
 
+#include "idzhook/idz-dll.h"
 #include "idzhook/jvs.h"
 
-#include "idzio/idzio.h"
-
 #include "jvs/jvs-bus.h"
 
 #include "util/dprintf.h"
@@ -56,9 +55,10 @@ HRESULT idz_jvs_init(struct jvs_node **out)
     HRESULT hr;
 
     assert(out != NULL);
+    assert(idz_dll.jvs_init != NULL);
 
     dprintf("JVS I/O: Starting Initial D Zero backend DLL\n");
-    hr = idz_io_jvs_init();
+    hr = idz_dll.jvs_init();
 
     if (FAILED(hr)) {
         dprintf("JVS I/O: Backend error, I/O disconnected; %x\n", (int) hr);
@@ -79,13 +79,15 @@ static void idz_jvs_read_switches(void *ctx, struct io3_switch_state *out)
     uint8_t gear;
 
     assert(out != NULL);
+    assert(idz_dll.jvs_read_buttons != NULL);
+    assert(idz_dll.jvs_read_shifter != NULL);
 
     opbtn = 0;
     gamebtn = 0;
     gear = 0;
 
-    idz_io_jvs_read_buttons(&opbtn, &gamebtn);
-    idz_io_jvs_read_shifter(&gear);
+    idz_dll.jvs_read_buttons(&opbtn, &gamebtn);
+    idz_dll.jvs_read_shifter(&gear);
 
     /* Update gameplay buttons */
 
@@ -142,9 +144,10 @@ static void idz_jvs_read_analogs(
     struct idz_io_analog_state state;
 
     assert(analogs != NULL);
+    assert(idz_dll.jvs_read_analogs != NULL);
 
     memset(&state, 0, sizeof(state));
-    idz_io_jvs_read_analogs(&state);
+    idz_dll.jvs_read_analogs(&state);
 
     if (nanalogs > 0) {
         analogs[0] = 0x8000 + state.wheel;
@@ -164,9 +167,11 @@ static void idz_jvs_read_coin_counter(
         uint8_t slot_no,
         uint16_t *out)
 {
+    assert(idz_dll.jvs_read_coin_counter != NULL);
+
     if (slot_no > 0) {
         return;
     }
 
-    idz_io_jvs_read_coin_counter(out);
+    idz_dll.jvs_read_coin_counter(out);
 }
diff --git a/idzhook/meson.build b/idzhook/meson.build
index e27007a..668ad8a 100644
--- a/idzhook/meson.build
+++ b/idzhook/meson.build
@@ -24,6 +24,8 @@ shared_library(
         'config.c',
         'config.h',
         'dllmain.c',
+        'idz-dll.c',
+        'idz-dll.h',
         'jvs.c',
         'jvs.h',
         'zinput.c',