diff --git a/cnpy.h b/cnpy.h
index 0d3bb4c..c7a0c23 100644
--- a/cnpy.h
+++ b/cnpy.h
@@ -247,10 +247,12 @@ namespace cnpy {
         }
         if(shape.size() == 1) dict += ",";
         dict += "), }";
-        //pad with spaces so that preamble+dict is modulo 16 bytes. preamble is 10 bytes. dict needs to end with \n
-        int remainder = 16 - (10 + dict.size()) % 16;
-        dict.insert(dict.end(),remainder,' ');
-        dict.back() = '\n';
+        // pad with spaces so that preamble+dict is modulo 64 bytes. preamble is
+        // 10 bytes. dict needs to end with \n
+        int remainder = 64 - (10 + dict.size() + 1) % 64;
+        dict.insert(dict.end(), remainder, ' ');
+        dict.push_back('\n');
+        assert((dict.size() + 10) % 64 == 0);
 
         std::vector<char> header;
         header += (char) 0x93;