diff --git a/src/libOpenImageIO/imagebuf.cpp b/src/libOpenImageIO/imagebuf.cpp
index f44091267b..583d8e2c4b 100644
--- a/src/libOpenImageIO/imagebuf.cpp
+++ b/src/libOpenImageIO/imagebuf.cpp
@@ -1448,7 +1448,8 @@ ImageBuf::write(ImageOutput* out, ProgressCallback progress_callback,
                         && progress_callback(
                             progress_callback_data,
                             (float)(z * outspec.height
-                                    + (isDecreasingY ? (outspec.height - y) : y))
+                                    + (isDecreasingY ? (outspec.height - 1 - y)
+                                                     : y))
                                 / (outspec.height * outspec.depth)))
                         return ok;
                 }
diff --git a/src/libOpenImageIO/imageoutput.cpp b/src/libOpenImageIO/imageoutput.cpp
index fb761a3033..34eb80ba32 100644
--- a/src/libOpenImageIO/imageoutput.cpp
+++ b/src/libOpenImageIO/imageoutput.cpp
@@ -544,7 +544,7 @@ ImageOutput::write_image(TypeDesc format, const void* data, stride_t xstride,
                     && progress_callback(
                         progress_callback_data,
                         (float)(z * m_spec.height
-                                + (isDecreasingY ? (m_spec.height - y) : y))
+                                + (isDecreasingY ? (m_spec.height - 1 - y) : y))
                             / (m_spec.height * m_spec.depth)))
                     return ok;
             }