diff --git a/.github/workflows/pony-lint.yml b/.github/workflows/pony-lint.yml
index 5e4e20b..8ddec33 100644
--- a/.github/workflows/pony-lint.yml
+++ b/.github/workflows/pony-lint.yml
@@ -17,7 +17,7 @@ jobs:
     name: Lint Pony source
     runs-on: ubuntu-latest
     container:
-      image: ghcr.io/ponylang/shared-docker-ci-standard-builder:release
+      image: ghcr.io/ponylang/shared-docker-ci-standard-builder:nightly
     steps:
       - uses: actions/checkout@v6.0.2
       - name: Lint
diff --git a/.github/workflows/pr.yml b/.github/workflows/pr.yml
index 028667d..a26b8b4 100644
--- a/.github/workflows/pr.yml
+++ b/.github/workflows/pr.yml
@@ -21,7 +21,7 @@ jobs:
     name: Test against recent ponyc release on Linux
     runs-on: ubuntu-latest
     container:
-      image: ghcr.io/ponylang/shared-docker-ci-standard-builder:release
+      image: ghcr.io/ponylang/shared-docker-ci-standard-builder:nightly
     steps:
       - uses: actions/checkout@v6.0.2
       - name: Test
@@ -33,7 +33,7 @@ jobs:
     steps:
       - uses: actions/checkout@v6.0.2
       - name: Install dependencies
-        run: bash .ci-scripts/macOS-install-pony-tools.bash release
+        run: bash .ci-scripts/macOS-install-pony-tools.bash nightly
       - name: Test
         run: |
           export PATH="$HOME/.local/share/ponyup/bin/:$PATH"
@@ -46,10 +46,10 @@ jobs:
       - uses: actions/checkout@v6.0.2
       - name: Test with most recent ponyc release
         run: |
-          Invoke-WebRequest https://dl.cloudsmith.io/public/ponylang/releases/raw/versions/latest/ponyc-x86-64-pc-windows-msvc.zip -OutFile C:\ponyc.zip;
+          Invoke-WebRequest https://dl.cloudsmith.io/public/ponylang/nightlies/raw/versions/latest/ponyc-x86-64-pc-windows-msvc.zip -OutFile C:\ponyc.zip;
           Expand-Archive -Path C:\ponyc.zip -DestinationPath C:\ponyc;
           $env:PATH = 'C:\ponyc\bin;' + $env:PATH;
-          Invoke-WebRequest https://dl.cloudsmith.io/public/ponylang/releases/raw/versions/latest/corral-x86-64-pc-windows-msvc.zip -OutFile C:\corral.zip;
+          Invoke-WebRequest https://dl.cloudsmith.io/public/ponylang/nightlies/raw/versions/latest/corral-x86-64-pc-windows-msvc.zip -OutFile C:\corral.zip;
           Expand-Archive -Path C:\corral.zip -DestinationPath C:\corral;
           $env:PATH = 'C:\corral\bin;' + $env:PATH;
           .\make.ps1 test
diff --git a/.release-notes/update-to-pony-0.78.0.md b/.release-notes/update-to-pony-0.78.0.md
new file mode 100644
index 0000000..cd80fbf
--- /dev/null
+++ b/.release-notes/update-to-pony-0.78.0.md
@@ -0,0 +1,3 @@
+## Update to work with Pony 0.78.0
+
+The minimum required ponyc version is now 0.78.0.
diff --git a/README.md b/README.md
index 7b276f7..bb77a6d 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@ Appdirs is an beta-level package.
 
 ## Installation
 
-* Requires ponyc 0.77.0 or later.
+* Requires ponyc 0.78.0 or later.
 * Install [corral](https://github.com/ponylang/corral)
 * `corral add github.com/ponylang/appdirs.git --version 0.2.0`
 * `corral fetch` to fetch your dependencies
diff --git a/appdirs/appdirs.pony b/appdirs/appdirs.pony
index b03ec36..642eff0 100644
--- a/appdirs/appdirs.pony
+++ b/appdirs/appdirs.pony
@@ -202,7 +202,7 @@ class AppDirs
       end
     match _app_version
     | let v: String =>
-      for i in Range[USize](
+      for i in Range[USize].till(
         0, os_specific_dirs.size())
       do
         os_specific_dirs(i)? =
@@ -225,7 +225,7 @@ class AppDirs
         end
       end
 
-    for idx in Range[USize](
+    for idx in Range[USize].till(
       0, data_dirs.size())
     do
       data_dirs(idx)? =
@@ -291,7 +291,7 @@ class AppDirs
 
     match _app_version
     | let v: String =>
-      for i in Range[USize](
+      for i in Range[USize].till(
         0, os_specific_dirs.size())
       do
         os_specific_dirs(i)? =
@@ -312,7 +312,7 @@ class AppDirs
         recover iso ["/etc/xdg"] end
       end
 
-    for idx in Range[USize](
+    for idx in Range[USize].till(
       0, config_dirs.size())
     do
       config_dirs(idx)? =