diff --git a/lib/scripts/legacy_lyxpreview2ppm.py b/lib/scripts/legacy_lyxpreview2ppm.py
index d16e86788f..e6d5371de2 100644
--- a/lib/scripts/legacy_lyxpreview2ppm.py
+++ b/lib/scripts/legacy_lyxpreview2ppm.py
@@ -114,13 +114,16 @@ def legacy_extract_metrics_info(log_file):
                 error("Unexpected data in %s\n%s" % (log_file, line))
 
             if snippet:
-                ascent  = string.atoi(match.group(2))
-                descent = string.atoi(match.group(3))
+                ascent  = string.atof(match.group(2))
+                descent = string.atof(match.group(3))
 
                 frac = 0.5
-                if ascent >= 0 and descent >= 0:
-                    ascent = float(ascent) + tp_ascent
-                    descent = float(descent) - tp_descent
+                if ascent == 0 and descent == 0:
+                    # This is an empty image, forbid its display
+                    frac = -1.0
+                elif ascent >= 0 or descent >= 0:
+                    ascent = ascent + tp_ascent
+                    descent = descent - tp_descent
 
                     if abs(ascent + descent) > 0.1:
                         frac = ascent / (ascent + descent)
@@ -225,7 +228,7 @@ def legacy_latex_file(latex_file, fg_color, bg_color):
 \definecolor{fg}{rgb}{%s}
 \definecolor{bg}{rgb}{%s}
 \pagecolor{bg}
-\usepackage[%s,lyx,tightpage]{preview}
+\usepackage[%s,tightpage]{preview}
 \makeatletter
 \g@addto@macro\preview{\begingroup\color{bg}\special{ps::clippath fill}\color{fg}}
 \g@addto@macro\endpreview{\endgroup}
diff --git a/lib/scripts/lyxpreview2bitmap.py b/lib/scripts/lyxpreview2bitmap.py
index ace46d21c6..5655bf36ca 100755
--- a/lib/scripts/lyxpreview2bitmap.py
+++ b/lib/scripts/lyxpreview2bitmap.py
@@ -137,7 +137,10 @@ def extract_metrics_info(dvipng_stdout):
         ascent  = string.atof(match.group(2))
 
         frac = 0.5
-        if ascent >= 0 or descent >= 0:
+        if ascent < 0:
+            # This is an empty image, forbid its display
+            frac = -1.0
+        elif ascent >= 0 or descent >= 0:
             if abs(ascent + descent) > 0.1:
                 frac = ascent / (ascent + descent)
 
diff --git a/src/graphics/PreviewImage.cpp b/src/graphics/PreviewImage.cpp
index 5eecfcc48a..8c3f31d44f 100644
--- a/src/graphics/PreviewImage.cpp
+++ b/src/graphics/PreviewImage.cpp
@@ -85,7 +85,7 @@ Dimension PreviewImage::dim() const
 	if (!image)
 		return dim;
 
-	dim.asc = int(pimpl_->ascent_frac_ * double(image->height()));
+	dim.asc = int(pimpl_->ascent_frac_ * double(image->height()) + 0.5);
 	dim.des = image->height() - dim.asc;
 	dim.wid = image->width();
 	return dim;
diff --git a/src/graphics/PreviewLoader.cpp b/src/graphics/PreviewLoader.cpp
index 649f4602f2..3fd8fef029 100644
--- a/src/graphics/PreviewLoader.cpp
+++ b/src/graphics/PreviewLoader.cpp
@@ -734,7 +734,8 @@ void PreviewLoader::Impl::finishedGenerating(pid_t pid, int retval)
 		double af = ascent_fractions[metrics_counter];
 
 		// Add the image to the cache only if it's actually present
-		if (file.isReadableFile()) {
+		// and not empty (an empty image is signaled by af < 0)
+		if (af >= 0 && file.isReadableFile()) {
 			PreviewImagePtr ptr(new PreviewImage(parent_, snip, file, af));
 			cache_[snip] = ptr;