diff --git a/riscos/bitmap.c b/riscos/bitmap.c
index 5ab2f20e5..486019396 100644
--- a/riscos/bitmap.c
+++ b/riscos/bitmap.c
@@ -252,7 +252,7 @@ void bitmap_overlay_sprite(struct bitmap *bitmap, const osspriteop_header *s)
 	assert(sprite_bpp(s) == 8);
 
 	if ((unsigned)s->mode & 0x80000000U)
-		alpha = true; 
+		alpha = true;
 
 	error = xosspriteop_read_sprite_info(osspriteop_PTR,
 			(osspriteop_area *)0x100,
@@ -376,7 +376,7 @@ bool bitmap_initialise(struct bitmap *bitmap)
 void bitmap_set_opaque(struct bitmap *bitmap, bool opaque)
 {
 	assert(bitmap);
-	
+
 	if (opaque)
 		bitmap->state |= BITMAP_OPAQUE;
 	else
@@ -459,7 +459,7 @@ char *bitmap_get_buffer(struct bitmap *bitmap)
 		bitmap->previous = NULL;
 		bitmap_head = bitmap;
 	}
-	
+
 	/* dynamically create the buffer */
 	if (!(bitmap->state & BITMAP_READY)) {
 		if (!bitmap_initialise(bitmap))
@@ -592,8 +592,8 @@ void bitmap_set_suspendable(struct bitmap *bitmap, void *private_word,
 		void (*invalidate)(struct bitmap *bitmap, void *private_word)) {
 	bitmap->private_word = private_word;
 	bitmap->invalidate = invalidate;
-	bitmap_suspendable++;		  
-}	
+	bitmap_suspendable++;
+}
 
 
 /**
@@ -644,7 +644,7 @@ void bitmap_maintain(void)
 		bitmap_maintenance_priority = false;
 		return;
 	}
-	
+
 	/* the fastest and easiest way to release memory is by suspending
 	 * images. as such, we try to do this first for as many images as
 	 * possible, potentially freeing up large amounts of memory */
@@ -659,7 +659,7 @@ void bitmap_maintain(void)
 				bitmap_direct_used -= 16 + 44 +
 					    bitmap->width * bitmap->height * 4;
 			  	bitmap_suspended++;
-			} 
+			}
 		}
 		return;
 	}
@@ -892,7 +892,7 @@ void bitmap_save_file(struct bitmap *bitmap)
 	os_error *error;
 	struct bitmap_compressed_header *header;
 
-	assert(bitmap->compressed || bitmap->sprite_area);
+	assert(bitmap && (bitmap->compressed || bitmap->sprite_area));
 
 	/* unmodified bitmaps will still have their file available */
 	if ((!(bitmap->state & BITMAP_MODIFIED)) && bitmap->filename[0]) {
@@ -907,6 +907,11 @@ void bitmap_save_file(struct bitmap *bitmap)
 
 	/* dump the data (compressed or otherwise) to disk */
 	filename = filename_request();
+	if (!filename) {
+		LOG(("filename_request failed"));
+		return;
+	}
+
 	strcpy(bitmap->filename, filename);
 	sprintf(bitmap_unixname, "%s/%s", TEMP_FILENAME_PREFIX,
 			bitmap->filename);
diff --git a/riscos/gui.c b/riscos/gui.c
index b6f74f79b..925659265 100644
--- a/riscos/gui.c
+++ b/riscos/gui.c
@@ -2164,20 +2164,22 @@ void ro_gui_view_source(struct content *content)
 		message.file_name[211] = '\0';
 		free(temp_name);
 	} else {
-		/* We cannot release the requested filename until after it has finished
-		   being used. As we can't easily find out when this is, we simply don't
-		   bother releasing it and simply allow it to be re-used next time NetSurf
-		   is started. The memory overhead from doing this is under 1 byte per
-		   filename. */
-		temp_name = filename_request();
-		if (!temp_name) {
+		/* We cannot release the requested filename until after it
+		 * has finished being used. As we can't easily find out when
+		 * this is, we simply don't bother releasing it and simply
+		 * allow it to be re-used next time NetSurf is started. The
+		 * memory overhead from doing this is under 1 byte per
+		 * filename. */
+		const char *filename = filename_request();
+		if (!filename) {
 			warn_user("NoMemory", 0);
 			return;
 		}
-		snprintf(full_name, 256, "%s/%s", TEMP_FILENAME_PREFIX, temp_name);
+		snprintf(full_name, 256, "%s/%s", TEMP_FILENAME_PREFIX,
+				filename);
 		full_name[255] = '\0';
-		r = __riscosify(full_name, 0, __RISCOSIFY_NO_SUFFIX, message.file_name,
-				212, 0);
+		r = __riscosify(full_name, 0, __RISCOSIFY_NO_SUFFIX,
+				message.file_name, 212, 0);
 		if (r == 0) {
 			LOG(("__riscosify failed"));
 			return;
@@ -2205,7 +2207,8 @@ void ro_gui_view_source(struct content *content)
 	message.pos.y = 0;
 	message.est_size = 0;
 	message.file_type = 0xfff;
-	ro_message_send_message(wimp_USER_MESSAGE_RECORDED, (wimp_message*)&message, 0,
+	ro_message_send_message(wimp_USER_MESSAGE_RECORDED,
+			(wimp_message*)&message, 0,
 			ro_gui_view_source_bounce);
 }
 
diff --git a/utils/filename.c b/utils/filename.c
index 32fbad793..82a0c9965 100644
--- a/utils/filename.c
+++ b/utils/filename.c
@@ -19,6 +19,7 @@
 #include <sys/stat.h>
 #include "netsurf/utils/filename.h"
 #include "netsurf/utils/log.h"
+#include "netsurf/utils/utils.h"
 
 #define FULL_WORD (unsigned int)4294967295
 /* '0' + '0' * 10 */
@@ -44,9 +45,9 @@ static bool filename_delete_recursive(char *folder);
 /**
  * Request a new, unique, filename.
  *
- * \return a pointer to a shared buffer containing the new filename
+ * \return a pointer to a shared buffer containing the new filename or NULL on failure
  */
-char *filename_request(void) {
+const char *filename_request(void) {
 	struct directory *dir;
 	int i = -1;
 
@@ -321,7 +322,8 @@ bool filename_delete_recursive(char *folder) {
  * Creates a new directory.
  *
  * \param  prefix  the prefix to use, or NULL to allocate a new one
- * \return a new directory structure, or NULL on memory exhaustion
+ * \return a new directory structure, or NULL on memory exhaustion or
+ * creation failure
  *
  * Empty directories are never deleted, except by an explicit call to
  * filename_flush().
@@ -384,14 +386,17 @@ static struct directory *filename_create_directory(const char *prefix) {
 				TEMP_FILENAME_PREFIX,
 				new_dir->prefix);
 		new_dir->prefix[8] = '/';
-		if (!mkdir(filename_directory, S_IRWXU))
-			return new_dir;
+		if (!is_dir(filename_directory)) {
+			if (!mkdir(filename_directory, S_IRWXU))
+				return new_dir;
 
-		/* the user has probably deleted the parent directory whilst
-		 * we are running if there is an error, so we don't report
-		 * this yet and try to create the structure normally. */
-		LOG(("Failed to create optimised structure '%s'",
-				filename_directory));
+			/* the user has probably deleted the parent directory
+			 * whilst we are running if there is an error, so we
+			 * don't report this yet and try to create the
+			 * structure normally. */
+			LOG(("Failed to create optimised structure '%s'",
+					filename_directory));
+		}
 	}
 
 	/* create the directory structure */
@@ -405,12 +410,15 @@ static struct directory *filename_create_directory(const char *prefix) {
 			*last_1++ = *last_2++;
 		if (*last_2) {
 			last_1[0] = '\0';
-			if (mkdir(filename_directory, S_IRWXU)) {
-				LOG(("Failed to create directory '%s'",
-						filename_directory));
-				return NULL;
+			if (!is_dir(filename_directory)) {
+				if (mkdir(filename_directory, S_IRWXU)) {
+					LOG(("Failed to create directory '%s'",
+							filename_directory));
+					return NULL;
+				}
 			}
 		}
 	}
+
 	return new_dir;
 }
diff --git a/utils/filename.h b/utils/filename.h
index ef5b7090a..dab072b08 100644
--- a/utils/filename.h
+++ b/utils/filename.h
@@ -16,7 +16,7 @@
 #define TEMP_FILENAME_PREFIX "/tmp/WWW/NetSurf/Cache"
 #endif
 
-char *filename_request(void);
+const char *filename_request(void);
 bool filename_claim(const char *filename);
 void filename_release(const char *filename);
 bool filename_initialise(void);