diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1acd87e77..b03f7894f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,6 +21,7 @@
 - Fix series detection for some bioformats files ([#1365](../../pull/1365), [#1367](../../pull/1367))
 - Fix time comparison in annotation history check ([#1369](../../pull/1369))
 - Fix an issue with apply a frame style to ome tiffs ([#1374](../../pull/1374))
+- Guard against bad tifffile magnification values ([#1376](../../pull/1376))
 
 ## 1.26.0
 
diff --git a/sources/tifffile/large_image_source_tifffile/__init__.py b/sources/tifffile/large_image_source_tifffile/__init__.py
index 2fbce1776..9aa70c18d 100644
--- a/sources/tifffile/large_image_source_tifffile/__init__.py
+++ b/sources/tifffile/large_image_source_tifffile/__init__.py
@@ -125,10 +125,12 @@ def __init__(self, path, **kwargs):  # noqa
         try:
             unit = {2: 25.4, 3: 10}[page.tags['ResolutionUnit'].value.real]
 
-            if page.tags['XResolution'].value[1] >= 100:
+            if (page.tags['XResolution'].value[0] and (
+                    page.tags['XResolution'].value[1] / page.tags['XResolution'].value[0]) >= 100):
                 self._mm_x = (unit * page.tags['XResolution'].value[1] /
                               page.tags['XResolution'].value[0])
-            if page.tags['YResolution'].value[1] >= 100:
+            if (page.tags['YResolution'].value[0] and (
+                    page.tags['YResolution'].value[1] / page.tags['YResolution'].value[0]) >= 100):
                 self._mm_y = (unit * page.tags['YResolution'].value[1] /
                               page.tags['YResolution'].value[0])
         except Exception: