--- exiv2-0.26.orig/src/basicio.cpp.orig	2017-04-26 21:16:21.000000000 +0200
+++ exiv2-0.26.orig/src/basicio.cpp	2018-01-12 17:11:54.815825700 +0100
@@ -1093,10 +1093,12 @@
     void MemIo::Impl::reserve(long wcount)
     {
         long need = wcount + idx_;
+        long    blockSize =     32*1024;   // 32768           `
+        long maxBlockSize = 4*1024*1024;
 
         if (!isMalloced_) {
-            // Minimum size for 1st block is 32kB
-            long size  = EXV_MAX(32768 * (1 + need / 32768), size_);
+            // Minimum size for 1st block
+            long size  = EXV_MAX(blockSize * (1 + need / blockSize), size_);
             byte* data = (byte*)std::malloc(size);
             std::memcpy(data, data_, size_);
             data_ = data;
@@ -1106,8 +1108,10 @@
 
         if (need > size_) {
             if (need > sizeAlloced_) {
-                // Allocate in blocks of 32kB
-                long want = 32768 * (1 + need / 32768);
+                blockSize = 2*sizeAlloced_ ;
+                if ( blockSize > maxBlockSize ) blockSize = maxBlockSize ;
+                // Allocate in blocks
+                long want      = blockSize * (1 + need / blockSize );
                 data_ = (byte*)std::realloc(data_, want);
                 sizeAlloced_ = want;
                 isMalloced_ = true;