diff --git a/apps/ios/SimpleXChat/ImageUtils.swift b/apps/ios/SimpleXChat/ImageUtils.swift
index 9702408c27..9bf15992db 100644
--- a/apps/ios/SimpleXChat/ImageUtils.swift
+++ b/apps/ios/SimpleXChat/ImageUtils.swift
@@ -101,17 +101,12 @@ public func resizeImageToDataSize(_ image: UIImage, maxDataSize: Int64, hasAlpha
 }
 
 public func resizeImageToStrSizeSync(_ image: UIImage, maxDataSize: Int64) -> String? {
-    var img = image
-    let hasAlpha = imageHasAlpha(image)
-    var str = compressImageStr(img, hasAlpha: hasAlpha)
-    var dataSize = str?.count ?? 0
-    while dataSize != 0 && dataSize > maxDataSize {
-        let ratio = sqrt(Double(dataSize) / Double(maxDataSize))
-        let clippedRatio = min(ratio, 2.0)
-        img = reduceSize(img, ratio: clippedRatio, hasAlpha: hasAlpha)
-        str = compressImageStr(img, hasAlpha: hasAlpha)
-        dataSize = str?.count ?? 0
-    }
+    // XXX: only needed when the original encoding isn't available
+    let tmpFile = generateNewFileName(getTempFilesDirectory().path + "/" + "resize", "png", fullPath: true)
+    saveFile(image.pngData(), tmpFile) // encode as png and let the backend deal with alpha and formats
+    let str = chat_resize_image_to_str_size(filePath, maxDataSize)
+    removeFile(tmpFile)
+    guard let dataSize = str?.count > 0 else { return nil }
     logger.debug("resizeImageToStrSize final \(dataSize)")
     return str
 }
diff --git a/src/Simplex/Chat/Mobile.hs b/src/Simplex/Chat/Mobile.hs
index 5d55b21fa6..87b7302177 100644
--- a/src/Simplex/Chat/Mobile.hs
+++ b/src/Simplex/Chat/Mobile.hs
@@ -21,6 +21,7 @@ import qualified Data.ByteString.Base64.URL as U
 import Data.ByteString.Char8 (ByteString)
 import qualified Data.ByteString.Char8 as B
 import qualified Data.ByteString.Lazy.Char8 as LB
+import Data.Either (fromRight)
 import Data.Functor (($>))
 import Data.List (find)
 import qualified Data.List.NonEmpty as L
@@ -198,7 +199,10 @@ cChatJsonLength s = fromIntegral . subtract 2 . LB.length . J.encode . safeDecod
 -- cChatResizeImageToDataSize :: CString -> CInt -> IO CString
 -- cChatResizeImageToDataSize path maxSize = error "todo"
 
--- | Downscale image at path until its data-uri encoding fits into specified size
+-- | Downscale image at path until its data-uri encoding fits into specified size.
+-- Returns data-uri/base64 encoded image as 0-terminated string.
+-- Empty result string means operation failure.
+-- The caller must free the result ptr.
 cChatResizeImageToStrSize :: CString -> CInt -> IO CString
 cChatResizeImageToStrSize fp' maxSize = do
   fp <- peekCString fp'
@@ -206,7 +210,7 @@ cChatResizeImageToStrSize fp' maxSize = do
     (ri, _) <- liftIOEither $ readResizeable fp
     let resized = resizeImageToStrSize (fromIntegral maxSize) ri
     if LB.length resized > fromIntegral maxSize then throwError "unable to fit" else pure resized
-  either (const $ pure nullPtr) newCStringFromLazyBS res
+  newCStringFromLazyBS $ fromRight "" res
 
 -- -- | Strip EXIF etc metadata from image, inlplace
 -- cChatStripImageMetadata :: CString -> IO CBool