diff --git a/libvips/arithmetic/project.c b/libvips/arithmetic/project.c
index 6b61686a..69cb28e9 100644
--- a/libvips/arithmetic/project.c
+++ b/libvips/arithmetic/project.c
@@ -97,7 +97,7 @@ histogram_new( VipsProject *project )
 	VipsStatistic *statistic = VIPS_STATISTIC( project ); 
 	VipsImage *in = statistic->ready; 
 	VipsBandFormat outfmt = vips_project_format_table[in->BandFmt];
-	int psize = vips__image_sizeof_bandformat[outfmt] * in->Bands; 
+	int psize = vips_format_sizeof( outfmt ) * in->Bands; 
 
 	Histogram *hist;
 
diff --git a/libvips/arithmetic/unaryconst.c b/libvips/arithmetic/unaryconst.c
index 9bc7f0f5..a0fe5063 100644
--- a/libvips/arithmetic/unaryconst.c
+++ b/libvips/arithmetic/unaryconst.c
@@ -92,8 +92,7 @@ make_pixel( VipsObject *obj,
 	VipsPel *q;
 	int i;
 
-	if( !(q = VIPS_ARRAY( obj, 
-		m * vips__image_sizeof_bandformat[fmt], VipsPel )) )
+	if( !(q = VIPS_ARRAY( obj, m * vips_format_sizeof( fmt ), VipsPel )) )
 		return( NULL );
 
         switch( fmt ) {
diff --git a/libvips/include/vips/image.h b/libvips/include/vips/image.h
index 3e1beea1..dfc3eba2 100644
--- a/libvips/include/vips/image.h
+++ b/libvips/include/vips/image.h
@@ -350,12 +350,10 @@ GType vips_image_get_type( void );
 /* Has to be guint64 and not size_t/off_t since we have to be able to address
  * huge images on platforms with 32-bit files.
  */
-extern const guint64 vips__image_sizeof_bandformat[];
-
 /* Pixel address calculation macros.
  */
 #define VIPS_IMAGE_SIZEOF_ELEMENT( I ) \
-	(vips__image_sizeof_bandformat[(I)->BandFmt])
+	(vips_format_sizeof((I)->BandFmt))
 #define VIPS_IMAGE_SIZEOF_PEL( I ) \
 	(VIPS_IMAGE_SIZEOF_ELEMENT( I ) * (I)->Bands)
 #define VIPS_IMAGE_SIZEOF_LINE( I ) \
diff --git a/libvips/include/vips/vips7compat.h b/libvips/include/vips/vips7compat.h
index 3bf8cdf5..03a76150 100644
--- a/libvips/include/vips/vips7compat.h
+++ b/libvips/include/vips/vips7compat.h
@@ -182,7 +182,7 @@ extern "C" {
 
 /* Renamed externs.
  */
-
+extern const guint64 vips__image_sizeof_bandformat[];
 #define im__sizeof_bandfmt vips__image_sizeof_bandformat
 
 /* Renamed functions.
diff --git a/libvips/iofuncs/header.c b/libvips/iofuncs/header.c
index b37dfb12..d38a8d87 100644
--- a/libvips/iofuncs/header.c
+++ b/libvips/iofuncs/header.c
@@ -165,10 +165,12 @@ static HeaderField old_double_field[] = {
 };
 
 /* This is used by (eg.) VIPS_IMAGE_SIZEOF_ELEMENT() to calculate object
- * size.
+ * size via vips_format_sizeof(). 
  *
  * It needs to be guint64 and not size_t since we use this as the basis for 
  * image address calcs and they have to be 64-bit, even on 32-bit machines. 
+ *
+ * Can't be static, we need this to be visible for vips7 compat.
  */
 const guint64 vips__image_sizeof_bandformat[] = {
 	sizeof( unsigned char ), 	/* VIPS_FORMAT_UCHAR */
@@ -187,15 +189,15 @@ const guint64 vips__image_sizeof_bandformat[] = {
  * vips_format_sizeof:
  * @format: format type
  *
- * Returns: number of bytes for a band format, or -1 on error.
+ * Returns: number of bytes for a band format.
  */
 guint64 
 vips_format_sizeof( VipsBandFormat format )
 {
-	return( (format < 0 || format > VIPS_FORMAT_DPCOMPLEX) ?
-		vips_error( "vips_format_sizeof", 
-			_( "unknown band format %d" ), format ), -1 :
-		vips__image_sizeof_bandformat[format] );
+	g_assert( format >= 0 && 
+		format < VIPS_FORMAT_LAST ); 
+
+	return( vips__image_sizeof_bandformat[format] );
 }
 
 #ifdef DEBUG