diff --git a/amex/ds.c b/amex/ds.c
index 59c6254..4c69f69 100644
--- a/amex/ds.c
+++ b/amex/ds.c
@@ -149,26 +149,25 @@ static HRESULT ds_handle_ioctl(struct irp *irp)
 
 static HRESULT ds_ioctl_get_geometry(struct irp *irp)
 {
-    DISK_GEOMETRY *out;
-
-    if (irp->read.nbytes < sizeof(*out)) {
-        dprintf("DS: Invalid ioctl response buffer size\n");
-
-        return HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER);
-    }
+    DISK_GEOMETRY out;
+    HRESULT hr;
 
     dprintf("DS: Get geometry\n");
 
-    out = (DISK_GEOMETRY *) irp->read.bytes;
-    out->Cylinders.QuadPart = 1;
-    out->MediaType = 0;
-    out->TracksPerCylinder = 1;
-    out->SectorsPerTrack = 2;
-    out->BytesPerSector = 32;
+    memset(&out, 0, sizeof(out));
+    out.Cylinders.QuadPart = 1;
+    out.MediaType = 0;
+    out.TracksPerCylinder = 1;
+    out.SectorsPerTrack = 2;
+    out.BytesPerSector = 32;
 
-    irp->read.pos = sizeof(*out);
+    hr = iobuf_write(&irp->read, &out, sizeof(out));
 
-    return S_OK;
+    if (FAILED(hr)) {
+        dprintf("DS: Get geometry failed: %08x\n", (int) hr);
+    }
+
+    return hr;
 }
 
 static HRESULT ds_ioctl_setup(struct irp *irp)
diff --git a/amex/eeprom.c b/amex/eeprom.c
index 4c1d1d5..aa004f3 100644
--- a/amex/eeprom.c
+++ b/amex/eeprom.c
@@ -118,28 +118,27 @@ static HRESULT eeprom_handle_ioctl(struct irp *irp)
 
 static HRESULT eeprom_ioctl_get_geometry(struct irp *irp)
 {
-    DISK_GEOMETRY *out;
-
-    if (irp->read.nbytes < sizeof(*out)) {
-        dprintf("EEPROM: Invalid ioctl response buffer size\n");
-
-        return HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER);
-    }
+    DISK_GEOMETRY out;
+    HRESULT hr;
 
     dprintf("EEPROM: Get geometry\n");
 
     /* Not the real values, just bullshitting something for now */
 
-    out = (DISK_GEOMETRY *) irp->read.bytes;
-    out->Cylinders.QuadPart = 0x800;
-    out->MediaType = 0;
-    out->TracksPerCylinder = 1;
-    out->SectorsPerTrack = 2;
-    out->BytesPerSector = 4;
+    memset(&out, 0, sizeof(out));
+    out.Cylinders.QuadPart = 0x800;
+    out.MediaType = 0;
+    out.TracksPerCylinder = 1;
+    out.SectorsPerTrack = 2;
+    out.BytesPerSector = 4;
 
-    irp->read.pos = sizeof(*out);
+    hr = iobuf_write(&irp->read, &out, sizeof(out));
 
-    return S_OK;
+    if (FAILED(hr)) {
+        dprintf("EEPROM: Get geometry failed: %08x\n", (int) hr);
+    }
+
+    return hr;
 }
 
 static HRESULT eeprom_handle_read(struct irp *irp)
diff --git a/amex/gpio.c b/amex/gpio.c
index 6f5c4da..cba3b7d 100644
--- a/amex/gpio.c
+++ b/amex/gpio.c
@@ -205,18 +205,17 @@ static HRESULT gpio_ioctl_get_psw(struct irp *irp)
 
 static HRESULT gpio_ioctl_describe(struct irp *irp)
 {
+    HRESULT hr;
+
     dprintf("GPIO: Describe GPIO ports\n");
 
-    if (irp->read.nbytes < sizeof(gpio_ports)) {
-        dprintf("GPIO: Descriptor read buffer too small\n");
+    hr = iobuf_write(&irp->read, &gpio_ports, sizeof(gpio_ports));
 
-        return HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER);
+    if (FAILED(hr)) {
+        dprintf("GPIO: Describe GPIO ports failed: %08x\n", (int) hr);
     }
 
-    memcpy(irp->read.bytes, &gpio_ports, sizeof(gpio_ports));
-    irp->read.pos = sizeof(gpio_ports);
-
-    return S_OK;
+    return hr;
 }
 
 static HRESULT gpio_ioctl_set_leds(struct irp *irp)
diff --git a/amex/sram.c b/amex/sram.c
index 790588b..1b8f81a 100644
--- a/amex/sram.c
+++ b/amex/sram.c
@@ -114,24 +114,23 @@ static HRESULT sram_handle_ioctl(struct irp *irp)
 
 static HRESULT sram_ioctl_get_geometry(struct irp *irp)
 {
-    DISK_GEOMETRY *out;
-
-    if (irp->read.nbytes < sizeof(*out)) {
-        dprintf("SRAM: Invalid ioctl response buffer size\n");
-
-        return HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER);
-    }
+    DISK_GEOMETRY out;
+    HRESULT hr;
 
     dprintf("SRAM: Get geometry\n");
 
-    out = (DISK_GEOMETRY *) irp->read.bytes;
-    out->Cylinders.QuadPart = 0x20000;
-    out->MediaType = 0;
-    out->TracksPerCylinder = 1;
-    out->SectorsPerTrack = 1;
-    out->BytesPerSector = 4;
+    memset(&out, 0, sizeof(out));
+    out.Cylinders.QuadPart = 0x20000;
+    out.MediaType = 0;
+    out.TracksPerCylinder = 1;
+    out.SectorsPerTrack = 1;
+    out.BytesPerSector = 4;
 
-    irp->read.pos = sizeof(*out);
+    hr = iobuf_write(&irp->read, &out, sizeof(out));
 
-    return S_OK;
+    if (FAILED(hr)) {
+        dprintf("SRAM: Get geometry failed: %08x\n", (int) hr);
+    }
+
+    return hr;
 }