diff --git a/pymake/pymake.py b/pymake/pymake.py
index ac84737..22ab447 100644
--- a/pymake/pymake.py
+++ b/pymake/pymake.py
@@ -54,6 +54,7 @@
 
 import argparse
 import os
+import pathlib as pl
 import shutil
 import sys
 import time
@@ -256,29 +257,41 @@ def compress_targets(self):
                     targets.append(target)
 
             # add code.json
-            if "code.json" not in targets:
-                targets.append("code.json")
+            if pl.Path("code.json").exists():
+                if "code.json" not in targets:
+                    targets.append("code.json")
 
             # delete the zip file if it exists
             if os.path.exists(zip_pth):
-                if self.verbose:
-                    msg = f"Deleting existing zipfile '{zip_pth}'"
-                    print(msg)
-                os.remove(zip_pth)
+                if self.keep:
+                    if self.verbose:
+                        print(
+                            "Appending files to existing "
+                            + f"zipfile '{zip_pth}'"
+                        )
+                else:
+                    if self.verbose:
+                        print(f"Deleting existing zipfile '{zip_pth}'")
+                    os.remove(zip_pth)
 
             # print a message describing the zip process
             if self.verbose:
-                msg = (
+                print(
                     f"Compressing files in '{appdir}' "
                     + f"directory to zip file '{zip_pth}'"
                 )
-                print(msg)
                 for idx, target in enumerate(targets):
-                    msg = f" {idx + 1:>3d}. adding " + f"'{target}' to zipfile"
-                    print(msg)
+                    print(
+                        f" {idx + 1:>3d}. adding " + f"'{target}' to zipfile"
+                    )
 
             # compress the compiled executables
-            if not zip_all(zip_pth, dir_pths=appdir, patterns=targets):
+            if not zip_all(
+                zip_pth,
+                dir_pths=appdir,
+                patterns=targets,
+                append=self.keep,
+            ):
                 self.returncode = 1
 
         return
diff --git a/pymake/utils/download.py b/pymake/utils/download.py
index c11df28..ea6d921 100644
--- a/pymake/utils/download.py
+++ b/pymake/utils/download.py
@@ -95,7 +95,13 @@ def extractall(self, path=None, members=None, pwd=None):
             self.extract(zipinfo, path, pwd)
 
     @staticmethod
-    def compressall(path, file_pths=None, dir_pths=None, patterns=None):
+    def compressall(
+        path,
+        file_pths=None,
+        dir_pths=None,
+        patterns=None,
+        append=False,
+    ):
         """Compress selected files or files in selected directories.
 
         Parameters
@@ -108,6 +114,9 @@ def compressall(path, file_pths=None, dir_pths=None, patterns=None):
             directory paths to include in the output zip file (default is None)
         patterns : str or list of str
             file patterns to include in the output zip file (default is None)
+        append : bool
+            boolean indicating if file paths should be appended to an existing
+            zip file
 
         Returns
         -------
@@ -159,21 +168,19 @@ def compressall(path, file_pths=None, dir_pths=None, patterns=None):
                     tlist.append(file_pth)
             file_pths = tlist
 
-        # write the zipfile
+        if append and pl.Path(path).exists():
+            mode = "a"
+        else:
+            mode = "w"
+
         success = True
         if len(file_pths) > 0:
-            zf = ZipFile(path, "w", ZIP_DEFLATED)
-
-            # write files to zip file
-            for file_pth in file_pths:
-                arcname = os.path.basename(file_pth)
-                zf.write(file_pth, arcname=arcname)
-
-            # close the zip file
-            zf.close()
+            with ZipFile(path, mode=mode, compression=ZIP_DEFLATED) as zf:
+                for file_pth in file_pths:
+                    arcname = os.path.basename(file_pth)
+                    zf.write(file_pth, arcname=arcname)
         else:
-            msg = "No files to add to the zip file"
-            print(msg)
+            print("No files to add to the zip file")
             success = False
 
         return success
@@ -471,7 +478,13 @@ def download_and_unzip(
     return success
 
 
-def zip_all(path, file_pths=None, dir_pths=None, patterns=None):
+def zip_all(
+    path,
+    file_pths=None,
+    dir_pths=None,
+    patterns=None,
+    append=False,
+):
     """Compress all files in the user-provided list of file paths and directory
     paths that match the provided file patterns.
 
@@ -487,13 +500,20 @@ def zip_all(path, file_pths=None, dir_pths=None, patterns=None):
     patterns : str or list
         file pattern or list of file patterns s to match to when creating a
         list of files that will be compressed
+    append : bool
+        boolean indicating if file paths should be appended to an existing
+        zip file
 
     Returns
     -------
 
     """
     return pymakeZipFile.compressall(
-        path, file_pths=file_pths, dir_pths=dir_pths, patterns=patterns
+        path,
+        file_pths=file_pths,
+        dir_pths=dir_pths,
+        patterns=patterns,
+        append=append,
     )