diff --git a/TODO b/TODO
index b521c35d..a033d7d3 100644
--- a/TODO
+++ b/TODO
@@ -1,11 +1,5 @@
-
-- easy to get a segv with Nicolas's interpolators, argh
-
-  just with float images?
-
-  try to_polar workspace, set LBB, zoom in and scroll around a bit
-
-
+- get some brightly coloured spots with nohalo / vsqbs on wobble.ws ... very
+  odd, the interpolation shouldn't change between bands
 
 - still not happy about float->int mask conversion in im_vips2mask.c
 
diff --git a/libvips/resample/bicubic.cpp b/libvips/resample/bicubic.cpp
index 238bf991..7525bc35 100644
--- a/libvips/resample/bicubic.cpp
+++ b/libvips/resample/bicubic.cpp
@@ -408,6 +408,17 @@ vips_interpolate_bicubic_interpolate( VipsInterpolate *interpolate,
 	const int bands = in->im->Bands;
 	const int lskip = VIPS_REGION_LSKIP( in );
 
+	g_assert( ix - 1 >= in->valid.left );
+	g_assert( iy - 1 >= in->valid.top );
+	g_assert( ix + 2 < VIPS_RECT_RIGHT( &in->valid ) );
+	g_assert( iy + 2 < VIPS_RECT_BOTTOM( &in->valid ) );
+
+	/* Confirm that absolute_x and absolute_y are >= 1, because of
+	 * window_offset.
+	 */
+	g_assert( x >= 1.0 );
+	g_assert( y >= 1.0 );
+
 #ifdef DEBUG
 	printf( "vips_interpolate_bicubic_interpolate: %g %g\n", x, y );
 	printf( "\tleft=%d, top=%d, width=%d, height=%d\n",
diff --git a/libvips/resample/interpolate.c b/libvips/resample/interpolate.c
index 42320cb4..d1de9d6f 100644
--- a/libvips/resample/interpolate.c
+++ b/libvips/resample/interpolate.c
@@ -513,6 +513,11 @@ vips_interpolate_bilinear_interpolate( VipsInterpolate *interpolate,
 
 	int z;
 
+	g_assert( (int) x >= in->valid.left );
+	g_assert( (int) y >= in->valid.top );
+	g_assert( (int) x + 1 < VIPS_RECT_RIGHT( &in->valid ) );
+	g_assert( (int) y + 1 < VIPS_RECT_BOTTOM( &in->valid ) );
+
 	SWITCH_INTERPOLATE( in->im->BandFmt,
 		BILINEAR_INT, BILINEAR_FLOAT );
 }
diff --git a/libvips/resample/lbb.cpp b/libvips/resample/lbb.cpp
index a678174b..17ba39bd 100644
--- a/libvips/resample/lbb.cpp
+++ b/libvips/resample/lbb.cpp
@@ -800,6 +800,11 @@ vips_interpolate_lbb_interpolate( VipsInterpolate* restrict interpolate,
     vips_band_format_iscomplex( in->im->BandFmt ) ? 
       2 * actual_bands : actual_bands;
 
+  g_assert( ix - 1 >= in->valid.left );
+  g_assert( iy - 1 >= in->valid.top );
+  g_assert( ix + 2 < VIPS_RECT_RIGHT( &in->valid ) );
+  g_assert( iy + 2 < VIPS_RECT_BOTTOM( &in->valid ) );
+
   /* Confirm that absolute_x and absolute_y are >= 1, see above. 
    */
   g_assert( absolute_x >= 1.0 );
diff --git a/libvips/resample/mapim.c b/libvips/resample/mapim.c
index f3f20b56..36431a10 100644
--- a/libvips/resample/mapim.c
+++ b/libvips/resample/mapim.c
@@ -189,7 +189,7 @@ vips_mapim_region_minmax( VipsRegion *region, VipsRect *r, VipsRect *bounds )
 			for( z = 0; z < ps; z++ )  \
 				q[z] = 0; \
 		} \
-		else  \
+		else \
 			interpolate( mapim->interpolate, q, ir[0], \
 				px + window_offset, py + window_offset ); \
 		\
@@ -244,8 +244,6 @@ vips_mapim_gen( VipsRegion *or, void *seq, void *a, void *b, gboolean *stop )
 	 */
 	bounds.width += window_size - 1;
 	bounds.height += window_size - 1;
-	bounds.left -= window_offset;
-	bounds.height -= window_offset;
 
 	/* Clip against the source image.
 	 */
diff --git a/libvips/resample/nohalo.cpp b/libvips/resample/nohalo.cpp
index 332b1786..01e5cf51 100644
--- a/libvips/resample/nohalo.cpp
+++ b/libvips/resample/nohalo.cpp
@@ -1493,8 +1493,8 @@ vips_interpolate_nohalo_interpolate( VipsInterpolate* restrict interpolate,
    *
    * It's 2 not 0 since we ask for a window_offset of 2 at the bottom.
    */
-  const int ix = (int) (absolute_x + 0.5);
-  const int iy = (int) (absolute_y + 0.5);
+  const int ix = (int) absolute_x;
+  const int iy = (int) absolute_y;
 
   /*
    * Move the pointer to (the first band of) the top/left pixel of the
@@ -1521,6 +1521,11 @@ vips_interpolate_nohalo_interpolate( VipsInterpolate* restrict interpolate,
     vips_band_format_iscomplex( in->im->BandFmt ) ? 
       2 * actual_bands : actual_bands;
 
+  g_assert( ix - 2 >= in->valid.left );
+  g_assert( iy - 2 >= in->valid.top );
+  g_assert( ix + 2 < VIPS_RECT_RIGHT( &in->valid ) );
+  g_assert( iy + 2 < VIPS_RECT_BOTTOM( &in->valid ) );
+
   /* Confirm that absolute_x and absolute_y are >= 2, see above. 
    */
   g_assert( absolute_x >= 2.0 );
diff --git a/libvips/resample/vsqbs.cpp b/libvips/resample/vsqbs.cpp
index 528b2b30..77e1ecb4 100644
--- a/libvips/resample/vsqbs.cpp
+++ b/libvips/resample/vsqbs.cpp
@@ -313,8 +313,8 @@ vips_interpolate_vsqbs_interpolate( VipsInterpolate* restrict interpolate,
    *
    * It's 1 not 0 since we ask for a window_offset of 1 at the bottom.
    */
-  const int ix = (int) (absolute_x + 0.5);
-  const int iy = (int) (absolute_y + 0.5);
+  const int ix = (int) absolute_x;
+  const int iy = (int) absolute_y;
 
   /*
    * Move the pointer to (the first band of) the top/left pixel of the
@@ -341,6 +341,11 @@ vips_interpolate_vsqbs_interpolate( VipsInterpolate* restrict interpolate,
     vips_band_format_iscomplex( in->im->BandFmt ) ? 
       2 * actual_bands : actual_bands;
 
+  g_assert( ix - 1 >= in->valid.left );
+  g_assert( iy - 1 >= in->valid.top );
+  g_assert( ix + 1 < VIPS_RECT_RIGHT( &in->valid ) );
+  g_assert( iy + 1 < VIPS_RECT_BOTTOM( &in->valid ) );
+
   /* Confirm that absolute_x and absolute_y are >= 1, see above. 
    */
   g_assert( absolute_x >= 1.0 );