diff --git a/BasiliskII/src/Unix/disk_sparsebundle.cpp b/BasiliskII/src/Unix/disk_sparsebundle.cpp
index ae96cffb..063e3296 100644
--- a/BasiliskII/src/Unix/disk_sparsebundle.cpp
+++ b/BasiliskII/src/Unix/disk_sparsebundle.cpp
@@ -255,39 +255,40 @@ static int try_open(const char *path, bool read_only, bool *locked) {
 	return fd;
 }
 
-disk_generic *disk_sparsebundle_factory(const char *path, bool read_only) {
+disk_generic::status disk_sparsebundle_factory(const char *path,
+		bool read_only, disk_generic **disk) {
 	// Does it look like a sparsebundle?
 	char buf[PATH_MAX + 1];
 	if (snprintf(buf, PATH_MAX, "%s/%s", path, "Info.plist") >= PATH_MAX)
-		return NULL;
+		return disk_generic::DISK_UNKNOWN;
 	
 	plist pl;
 	if (!pl.open(buf))
-		return NULL;	
+		return disk_generic::DISK_UNKNOWN;
 	
 	const char *type;
 	if (!(type = pl.str_val("diskimage-bundle-type")))
-		return NULL;
+		return disk_generic::DISK_UNKNOWN;
 	if (strcmp(type, "com.apple.diskimage.sparsebundle") != 0)
-		return NULL;
+		return disk_generic::DISK_UNKNOWN;
 	
 	
 	// Find the sparsebundle parameters
 	loff_t version, band_size, total_size;
 	if (!pl.int_val("bundle-backingstore-version", &version) || version != 1) {
 		fprintf(stderr, "sparsebundle: Bad version\n");
-		return NULL;
+		return disk_generic::DISK_UNKNOWN;
 	}
 	if (!pl.int_val("band-size", &band_size)
 			|| !pl.int_val("size", &total_size)) {
 		fprintf(stderr, "sparsebundle: Can't find size\n");
-		return NULL;
+		return disk_generic::DISK_INVALID;
 	}
 	
 	
 	// Check if we can open it
 	if (snprintf(buf, PATH_MAX, "%s/%s", path, "token") >= PATH_MAX)
-		return NULL;
+		return disk_generic::DISK_INVALID;
 	bool locked = false;
 	int token = try_open(buf, read_only, &locked);
 	if (token == -1 && !read_only) { // try again, read-only
@@ -301,13 +302,14 @@ disk_generic *disk_sparsebundle_factory(const char *path, bool read_only) {
 			fprintf(stderr, "sparsebundle: Refusing to double-mount\n");
 		else
 			perror("sparsebundle: open failed:");
-		return NULL;
+		return disk_generic::DISK_INVALID;
 	}
 	
 	
 	// We're good to go!
 	if (snprintf(buf, PATH_MAX, "%s/%s", path, "bands") >= PATH_MAX)
-		return NULL;
-	return new disk_sparsebundle(buf, token, read_only, band_size,
+		return disk_generic::DISK_INVALID;
+	*disk = new disk_sparsebundle(buf, token, read_only, band_size,
 		total_size);
+	return disk_generic::DISK_VALID;
 }
diff --git a/BasiliskII/src/Unix/disk_unix.h b/BasiliskII/src/Unix/disk_unix.h
index fb472aa1..6c427881 100644
--- a/BasiliskII/src/Unix/disk_unix.h
+++ b/BasiliskII/src/Unix/disk_unix.h
@@ -24,6 +24,12 @@
 #include "sysdeps.h"
 
 struct disk_generic {
+	enum status {
+		DISK_UNKNOWN,
+		DISK_INVALID,
+		DISK_VALID,
+	};
+	
 	disk_generic() { }
 	virtual ~disk_generic() { };
 	
@@ -33,7 +39,8 @@ struct disk_generic {
 	virtual loff_t size() = 0;
 };
 
-typedef disk_generic *(disk_factory)(const char *path, bool read_only);
+typedef disk_generic::status (disk_factory)(const char *path, bool read_only,
+	disk_generic **disk);
 
 extern disk_factory disk_sparsebundle_factory;
 extern disk_factory disk_vhd_factory;
diff --git a/BasiliskII/src/Unix/sys_unix.cpp b/BasiliskII/src/Unix/sys_unix.cpp
index dc7f07be..0dc50826 100644
--- a/BasiliskII/src/Unix/sys_unix.cpp
+++ b/BasiliskII/src/Unix/sys_unix.cpp
@@ -604,8 +604,11 @@ void *Sys_open(const char *name, bool read_only)
 
 
 	for (disk_factory **f = disk_factories; *f; ++f) {
-		disk_generic *generic = (*f)(name, read_only);
-		if (generic) {
+		disk_generic *generic;
+		disk_generic::status st = (*f)(name, read_only, &generic);
+		if (st == disk_generic::DISK_INVALID)
+			return NULL;
+		if (st == disk_generic::DISK_VALID) {
 			mac_file_handle *fh = open_filehandle(name);
 			fh->generic_disk = generic;
 			fh->file_size = generic->size();
diff --git a/BasiliskII/src/Unix/vhd_unix.cpp b/BasiliskII/src/Unix/vhd_unix.cpp
index bbd506b5..45f04e85 100644
--- a/BasiliskII/src/Unix/vhd_unix.cpp
+++ b/BasiliskII/src/Unix/vhd_unix.cpp
@@ -32,7 +32,8 @@ extern "C" {
 #define DEBUG 0
 #include "debug.h"
 
-static void *vhd_unix_open(const char *name, int *size, bool read_only)
+static disk_generic::status vhd_unix_open(const char *name, int *size,
+	bool read_only, vhd_context_t **ctx)
 {
 	int amode = read_only ? R_OK : (R_OK | W_OK);
 	int fid;
@@ -42,12 +43,12 @@ static void *vhd_unix_open(const char *name, int *size, bool read_only)
 
 	if (access(name, amode)) {
 		D(bug("vhd open -- incorrect permissions %s\n", name));
-		return NULL;
+		return disk_generic::DISK_UNKNOWN;
 	}
   
 	if (! (fid = open(name, O_RDONLY))) { 
 		D(bug("vhd open -- couldn't open file %s\n", name));
-		return NULL;
+		return disk_generic::DISK_UNKNOWN;
 	} 
 	else {
 		char buf[9];
@@ -56,7 +57,7 @@ static void *vhd_unix_open(const char *name, int *size, bool read_only)
 		close(fid);
 		if (strcmp("conectix", buf) != 0) {
 			D(bug("vhd open -- not vhd magic = %s\n", buf));
-			return NULL;
+			return disk_generic::DISK_UNKNOWN;
 		}
 		if (vhd = (vhd_context_t *) malloc(sizeof(vhd_context_t))) {
 			int err;
@@ -64,17 +65,18 @@ static void *vhd_unix_open(const char *name, int *size, bool read_only)
 								VHD_OPEN_RDONLY : VHD_OPEN_RDWR)) {
 				D(bug("vhd_open failed (%d)\n", err));
 				free(vhd);
-				return NULL;
+				return disk_generic::DISK_INVALID;
 			} 
 			else {
 				*size = (int) vhd->footer.curr_size;
 				printf("VHD Open %s\n", name);
-				return (void *) vhd;
+				*ctx = vhd;
+				return disk_generic::DISK_VALID;
 			}
 		}
 		else {
 			D(bug("vhd open -- malloc failed\n"));
-			return NULL;
+			return disk_generic::DISK_INVALID;
 		}
 	}
 }
@@ -147,10 +149,12 @@ protected:
 	loff_t file_size;
 };
 
-disk_generic *disk_vhd_factory(const char *path, bool read_only) {
+disk_generic::status disk_vhd_factory(const char *path,
+		bool read_only, disk_generic **disk) {
 	int size;
-	vhd_context_t *ctx = (vhd_context_t*)vhd_unix_open(path, &size, read_only);
-	if (!ctx)
-		return NULL;
-	return new disk_vhd(ctx, read_only, size);
+	vhd_context_t *ctx = NULL;
+	disk_generic::status st = vhd_unix_open(path, &size, read_only, &ctx);
+	if (st == disk_generic::DISK_VALID)
+		*disk = new disk_vhd(ctx, read_only, size);
+	return st;
 }