diff --git a/src/arch/i386/prefix/libprefix.S b/src/arch/i386/prefix/libprefix.S
index f5f66919..eeed0ada 100644
--- a/src/arch/i386/prefix/libprefix.S
+++ b/src/arch/i386/prefix/libprefix.S
@@ -443,6 +443,8 @@ install:
 	xorl	%esi, %esi
 	/* Image destination = default */
 	xorl	%edi, %edi
+	/* Allow relocation */
+	clc
 	/* Install text and data segments */
 	call	install_prealloc
 	/* Restore registers and return */
@@ -461,6 +463,7 @@ install:
  *   %bx  : .data16 segment address
  *   %esi : Image source physical address (or zero for %cs:0000)
  *   %edi : Decompression temporary area physical address (or zero for default)
+ *   CF set : Avoid relocating to top of memory
  * Corrupts:
  *   none
  ****************************************************************************
@@ -473,9 +476,8 @@ install_prealloc:
 	pushal
 	pushw	%ds
 	pushw	%es
-
-	/* Sanity: clear the direction flag asap */
-	cld
+	cld			/* Sanity: clear the direction flag asap */
+	pushfw
 
 	/* Copy decompression temporary area physical address to %ebp */
 	movl	%edi, %ebp
@@ -570,6 +572,11 @@ a20_death_message:
 	movl	%ebp, %edi
 	lcall	*init_librm_vector
 
+	/* Skip relocation if CF was set on entry */
+	popfw
+	pushfw
+	jc	skip_relocate
+
 	/* Call relocate() to determine target address for relocation.
 	 * relocate() will return with %esi, %edi and %ecx set up
 	 * ready for the copy to the new location.
@@ -588,9 +595,11 @@ a20_death_message:
 
 	/* Initialise librm at new location */
 	lcall	*init_librm_vector
+skip_relocate:
 #endif
 
 	/* Restore registers */
+	popfw
 	popw	%es
 	popw	%ds
 	popal
diff --git a/src/arch/i386/prefix/romprefix.S b/src/arch/i386/prefix/romprefix.S
index 2858cb3f..27eda346 100644
--- a/src/arch/i386/prefix/romprefix.S
+++ b/src/arch/i386/prefix/romprefix.S
@@ -407,6 +407,7 @@ no_pmm:
 	 * picked up by the initial shell prompt, and we will drop
 	 * into a shell.
 	 */
+	stc			/* Inhibit relocation */
 	pushw	%cs
 	call	exec
 2:
@@ -597,6 +598,7 @@ bbs_version:
  * Called by the PnP BIOS when it wants to boot us.
  */
 bev_entry:
+	clc			/* Allow relocation */
 	pushw	%cs
 	call	exec
 	lret
@@ -631,6 +633,7 @@ int19_entry:
 	/* Leave keypress in buffer and start iPXE.  The keypress will
 	 * cause the usual initial Ctrl-B prompt to be skipped.
 	 */
+	clc			/* Allow relocation */
 	pushw	%cs
 	call	exec
 1:	/* Try to call original INT 19 vector */
@@ -662,6 +665,9 @@ exec:	/* Set %ds = %cs */
 	pushw	%cs
 	popw	%ds
 
+	/* Preserve state of CF */
+	lahf
+
 	/* Print message as soon as possible */
 	movw	$prodstr, %si
 	xorw	%di, %di
@@ -675,14 +681,17 @@ exec:	/* Set %ds = %cs */
 	movw	%sp, %bp
 
 	/* Obtain a reasonably-sized temporary stack */
-	xorw	%ax, %ax
-	movw	%ax, %ss
+	xorw	%bx, %bx
+	movw	%bx, %ss
 	movw	$0x7c00, %sp
 
 	/* Install iPXE */
+	sahf
+	pushfw
+	call	alloc_basemem
+	popfw
 	movl	image_source, %esi
 	movl	decompress_to, %edi
-	call	alloc_basemem
 	call	install_prealloc
 
 	/* Print message indicating successful installation */
diff --git a/src/arch/i386/prefix/undiloader.S b/src/arch/i386/prefix/undiloader.S
index 36c1bef3..6fab3a34 100644
--- a/src/arch/i386/prefix/undiloader.S
+++ b/src/arch/i386/prefix/undiloader.S
@@ -28,6 +28,7 @@ undiloader:
 	movw	%es:14(%di), %ax
 	movl	image_source, %esi
 	movl	decompress_to, %edi
+	clc			/* Allow relocation */
 	call	install_prealloc
 	popw	%di
 	/* Call UNDI loader C code */