diff --git a/src/core/nvo.c b/src/core/nvo.c
index 1a886c0f8..9b325db75 100644
--- a/src/core/nvo.c
+++ b/src/core/nvo.c
@@ -133,7 +133,8 @@ static void nvo_init_dhcpopts ( struct nvo_block *nvo ) {
 		memset ( nvo->data, 0, nvo->total_len );
 	}
 
-	dhcpopt_init ( &nvo->dhcpopts, options_data, options_len );
+	dhcpopt_init ( &nvo->dhcpopts, options_data, options_len,
+		       dhcpopt_no_realloc );
 }
 
 /**
diff --git a/src/include/ipxe/dhcpopts.h b/src/include/ipxe/dhcpopts.h
index d88036e3a..fe07d903d 100644
--- a/src/include/ipxe/dhcpopts.h
+++ b/src/include/ipxe/dhcpopts.h
@@ -19,16 +19,23 @@ struct dhcp_options {
 	size_t used_len;
 	/** Option block allocated length */
 	size_t alloc_len;
+	/** Reallocate option block raw data
+	 *
+	 * @v options		DHCP option block
+	 * @v len		New length
+	 * @ret rc		Return status code
+	 */
+	int ( * realloc ) ( struct dhcp_options *options, size_t len );
 };
 
 extern int dhcpopt_store ( struct dhcp_options *options, unsigned int tag,
 			   const void *data, size_t len );
-extern int dhcpopt_extensible_store ( struct dhcp_options *options,
-				      unsigned int tag,
-				      const void *data, size_t len );
 extern int dhcpopt_fetch ( struct dhcp_options *options, unsigned int tag,
 			   void *data, size_t len );
 extern void dhcpopt_init ( struct dhcp_options *options,
-			   void *data, size_t alloc_len );
+			   void *data, size_t alloc_len,
+			   int ( * realloc ) ( struct dhcp_options *options,
+					       size_t len ) );
+extern int dhcpopt_no_realloc ( struct dhcp_options *options, size_t len );
 
 #endif /* _IPXE_DHCPOPTS_H */
diff --git a/src/net/dhcpopts.c b/src/net/dhcpopts.c
index 214a8244c..d1330eae5 100644
--- a/src/net/dhcpopts.c
+++ b/src/net/dhcpopts.c
@@ -169,6 +169,17 @@ static int find_dhcp_option_with_encap ( struct dhcp_options *options,
 	return -ENOENT;
 }
 
+/**
+ * Refuse to reallocate DHCP option block
+ *
+ * @v options		DHCP option block
+ * @v len		New length
+ * @ret rc		Return status code
+ */
+int dhcpopt_no_realloc ( struct dhcp_options *options, size_t len ) {
+	return ( ( len <= options->alloc_len ) ? 0 : -ENOSPC );
+}
+
 /**
  * Resize a DHCP option
  *
@@ -177,46 +188,44 @@ static int find_dhcp_option_with_encap ( struct dhcp_options *options,
  * @v encap_offset	Offset of encapsulating offset (or -ve for none)
  * @v old_len		Old length (including header)
  * @v new_len		New length (including header)
- * @v can_realloc	Can reallocate options data if necessary
  * @ret rc		Return status code
  */
 static int resize_dhcp_option ( struct dhcp_options *options,
 				int offset, int encap_offset,
-				size_t old_len, size_t new_len,
-				int can_realloc ) {
+				size_t old_len, size_t new_len ) {
 	struct dhcp_option *encapsulator;
 	struct dhcp_option *option;
 	ssize_t delta = ( new_len - old_len );
-	size_t new_options_len;
+	size_t old_alloc_len;
+	size_t new_used_len;
 	size_t new_encapsulator_len;
-	void *new_data;
 	void *source;
 	void *dest;
 	void *end;
+	int rc;
 
-	/* Check for sufficient space, and update length fields */
+	/* Check for sufficient space */
 	if ( new_len > DHCP_MAX_LEN ) {
 		DBGC ( options, "DHCPOPT %p overlength option\n", options );
 		return -ENOSPC;
 	}
-	new_options_len = ( options->used_len + delta );
-	if ( new_options_len > options->alloc_len ) {
-		/* Reallocate options block if allowed to do so. */
-		if ( can_realloc ) {
-			new_data = realloc ( options->data, new_options_len );
-			if ( ! new_data ) {
-				DBGC ( options, "DHCPOPT %p could not "
-				       "reallocate to %zd bytes\n", options,
-				       new_options_len );
-				return -ENOMEM;
-			}
-			options->data = new_data;
-			options->alloc_len = new_options_len;
-		} else {
-			DBGC ( options, "DHCPOPT %p out of space\n", options );
-			return -ENOMEM;
+	new_used_len = ( options->used_len + delta );
+
+	/* Expand options block, if necessary */
+	if ( new_used_len > options->alloc_len ) {
+		/* Reallocate options block */
+		old_alloc_len = options->alloc_len;
+		if ( ( rc = options->realloc ( options, new_used_len ) ) != 0 ){
+			DBGC ( options, "DHCPOPT %p could not reallocate to "
+			       "%zd bytes\n", options, new_used_len );
+			return rc;
 		}
+		/* Clear newly allocated space */
+		memset ( ( options->data + old_alloc_len ), 0,
+			 ( options->alloc_len - old_alloc_len ) );
 	}
+
+	/* Update encapsulator, if applicable */
 	if ( encap_offset >= 0 ) {
 		encapsulator = dhcp_option ( options, encap_offset );
 		new_encapsulator_len = ( encapsulator->len + delta );
@@ -227,7 +236,9 @@ static int resize_dhcp_option ( struct dhcp_options *options,
 		}
 		encapsulator->len = new_encapsulator_len;
 	}
-	options->used_len = new_options_len;
+
+	/* Update used length */
+	options->used_len = new_used_len;
 
 	/* Move remainder of option data */
 	option = dhcp_option ( options, offset );
@@ -236,6 +247,15 @@ static int resize_dhcp_option ( struct dhcp_options *options,
 	end = ( options->data + options->alloc_len );
 	memmove ( dest, source, ( end - dest ) );
 
+	/* Shrink options block, if applicable */
+	if ( new_used_len < options->alloc_len ) {
+		if ( ( rc = options->realloc ( options, new_used_len ) ) != 0 ){
+			DBGC ( options, "DHCPOPT %p could not reallocate to "
+			       "%zd bytes\n", options, new_used_len );
+			return rc;
+		}
+	}
+
 	return 0;
 }
 
@@ -246,7 +266,6 @@ static int resize_dhcp_option ( struct dhcp_options *options,
  * @v tag		DHCP option tag
  * @v data		New value for DHCP option
  * @v len		Length of value, in bytes
- * @v can_realloc	Can reallocate options data if necessary
  * @ret offset		Offset of DHCP option, or negative error
  *
  * Sets the value of a DHCP option within the options block.  The
@@ -258,9 +277,8 @@ static int resize_dhcp_option ( struct dhcp_options *options,
  * be left with its original value.
  */
 static int set_dhcp_option ( struct dhcp_options *options, unsigned int tag,
-			     const void *data, size_t len,
-			     int can_realloc ) {
-	static const uint8_t empty_encapsulator[] = { DHCP_END };
+			     const void *data, size_t len ) {
+	static const uint8_t empty_encap[] = { DHCP_END };
 	int offset;
 	int encap_offset = -1;
 	int creation_offset;
@@ -291,10 +309,12 @@ static int set_dhcp_option ( struct dhcp_options *options, unsigned int tag,
 
 	/* Ensure that encapsulator exists, if required */
 	if ( encap_tag ) {
-		if ( encap_offset < 0 )
-			encap_offset = set_dhcp_option ( options, encap_tag,
-							 empty_encapsulator, 1,
-							 can_realloc );
+		if ( encap_offset < 0 ) {
+			encap_offset =
+				set_dhcp_option ( options, encap_tag,
+						  empty_encap,
+						  sizeof ( empty_encap ) );
+		}
 		if ( encap_offset < 0 )
 			return encap_offset;
 		creation_offset = ( encap_offset + DHCP_OPTION_HEADER_LEN );
@@ -306,8 +326,7 @@ static int set_dhcp_option ( struct dhcp_options *options, unsigned int tag,
 
 	/* Resize option to fit new data */
 	if ( ( rc = resize_dhcp_option ( options, offset, encap_offset,
-					 old_len, new_len,
-					 can_realloc ) ) != 0 )
+					 old_len, new_len ) ) != 0 )
 		return rc;
 
 	/* Copy new data into option, if applicable */
@@ -322,7 +341,7 @@ static int set_dhcp_option ( struct dhcp_options *options, unsigned int tag,
 	if ( encap_offset >= 0 ) {
 		option = dhcp_option ( options, encap_offset );
 		if ( option->len <= 1 )
-			set_dhcp_option ( options, encap_tag, NULL, 0, 0 );
+			set_dhcp_option ( options, encap_tag, NULL, 0 );
 	}
 
 	return offset;
@@ -341,26 +360,7 @@ int dhcpopt_store ( struct dhcp_options *options, unsigned int tag,
 		    const void *data, size_t len ) {
 	int offset;
 
-	offset = set_dhcp_option ( options, tag, data, len, 0 );
-	if ( offset < 0 )
-		return offset;
-	return 0;
-}
-
-/**
- * Store value of DHCP option setting, extending options block if necessary
- *
- * @v options		DHCP option block
- * @v tag		Setting tag number
- * @v data		Setting data, or NULL to clear setting
- * @v len		Length of setting data
- * @ret rc		Return status code
- */
-int dhcpopt_extensible_store ( struct dhcp_options *options, unsigned int tag,
-			       const void *data, size_t len ) {
-	int offset;
-
-	offset = set_dhcp_option ( options, tag, data, len, 1 );
+	offset = set_dhcp_option ( options, tag, data, len );
 	if ( offset < 0 )
 		return offset;
 	return 0;
@@ -428,16 +428,19 @@ static void dhcpopt_update_used_len ( struct dhcp_options *options ) {
  * @v options		Uninitialised DHCP option block
  * @v data		Memory for DHCP option data
  * @v alloc_len		Length of memory for DHCP option data
+ * @v realloc		DHCP option block reallocator
  *
  * The memory content must already be filled with valid DHCP options.
  * A zeroed block counts as a block of valid DHCP options.
  */
-void dhcpopt_init ( struct dhcp_options *options, void *data,
-		    size_t alloc_len ) {
+void dhcpopt_init ( struct dhcp_options *options, void *data, size_t alloc_len,
+		    int ( * realloc ) ( struct dhcp_options *options,
+					size_t len ) ) {
 
 	/* Fill in fields */
 	options->data = data;
 	options->alloc_len = alloc_len;
+	options->realloc = realloc;
 
 	/* Update length */
 	dhcpopt_update_used_len ( options );
diff --git a/src/net/dhcppkt.c b/src/net/dhcppkt.c
index e043bb5d4..237c3e2cf 100644
--- a/src/net/dhcppkt.c
+++ b/src/net/dhcppkt.c
@@ -267,7 +267,8 @@ void dhcppkt_init ( struct dhcp_packet *dhcppkt, struct dhcphdr *data,
 	ref_init ( &dhcppkt->refcnt, NULL );
 	dhcppkt->dhcphdr = data;
 	dhcpopt_init ( &dhcppkt->options, &dhcppkt->dhcphdr->options,
-		       ( len - offsetof ( struct dhcphdr, options ) ) );
+		       ( len - offsetof ( struct dhcphdr, options ) ),
+		       dhcpopt_no_realloc );
 	settings_init ( &dhcppkt->settings,
 			&dhcppkt_settings_operations, &dhcppkt->refcnt, 0 );
 }