diff --git a/src/img2pdf.py b/src/img2pdf.py
index f851d92..94bb4de 100755
--- a/src/img2pdf.py
+++ b/src/img2pdf.py
@@ -1311,7 +1311,22 @@ def get_imgmetadata(
     else:
         imgwidthpx, imgheightpx = imgdata.size
 
-        ndpi = imgdata.info.get("dpi", (default_dpi, default_dpi))
+        ndpi = imgdata.info.get("dpi")
+        # the PNG plugin of PIL adds the undocumented "aspect" field instead of
+        # the "dpi" field if the PNG pHYs chunk unit is not set to meters
+        if (
+            ndpi is None
+            and imgformat == ImageFormat.PNG
+            and imgdata.info.get("aspect") is not None
+        ):
+            aspect = imgdata.info["aspect"]
+            # make sure not to go below the default dpi
+            if aspect[0] > aspect[1]:
+                ndpi = (default_dpi * aspect[0] / aspect[1], default_dpi)
+            else:
+                ndpi = (default_dpi, default_dpi * aspect[1] / aspect[0])
+        else:
+            ndpi = (default_dpi, default_dpi)
         # In python3, the returned dpi value for some tiff images will
         # not be an integer but a float. To make the behaviour of
         # img2pdf the same between python2 and python3, we convert that