diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4b9c151a..eaf9acb7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,10 @@ and this project adheres to
 
 - Add support for arm64.
 
+### Changed
+
+- Fail on missing required input instead of warning.
+
 ## [2.0.5]
 
 ### Changed
diff --git a/dist/index.js b/dist/index.js
index 6e122425..6261302f 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -95134,32 +95134,39 @@ const CYGWIN_ROOT = external_path_.join("D:", "cygwin");
 const CYGWIN_ROOT_BIN = external_path_.join(CYGWIN_ROOT, "bin");
 const CYGWIN_ROOT_WRAPPERBIN = external_path_.join(CYGWIN_ROOT, "wrapperbin");
 const CACHE_PREFIX = lib_core.getInput("cache-prefix", {
+    required: false,
     trimWhitespace: true,
 });
 const constants_GITHUB_TOKEN = lib_core.getInput("github-token", {
+    required: false,
     trimWhitespace: true,
 });
 const DUNE_CACHE = lib_core.getBooleanInput("dune-cache", {
+    required: false,
     trimWhitespace: true,
 });
 const OCAML_COMPILER = lib_core.getInput("ocaml-compiler", {
+    required: true,
     trimWhitespace: true,
 });
 const OPAM_DEPEXT = lib_core.getBooleanInput("opam-depext", {
+    required: false,
     trimWhitespace: true,
 });
-const OPAM_DEPEXT_FLAGS = lib_core.getInput("opam-depext-flags", { trimWhitespace: true })
+const OPAM_DEPEXT_FLAGS = lib_core.getInput("opam-depext-flags", { required: false, trimWhitespace: true })
     .split(",")
     .map((f) => f.trim())
     .filter((f) => f.length > 0);
-const OPAM_DISABLE_SANDBOXING = lib_core.getBooleanInput("opam-disable-sandboxing", { trimWhitespace: true });
+const OPAM_DISABLE_SANDBOXING = lib_core.getBooleanInput("opam-disable-sandboxing", { required: false, trimWhitespace: true });
 const OPAM_LOCAL_PACKAGES = lib_core.getInput("opam-local-packages", {
+    required: false,
     trimWhitespace: true,
 });
 const OPAM_PIN = lib_core.getBooleanInput("opam-pin", {
+    required: false,
     trimWhitespace: true,
 });
-const repositories_yaml = dist/* parse */.Qc(lib_core.getInput("opam-repositories", { trimWhitespace: true }));
+const repositories_yaml = dist/* parse */.Qc(lib_core.getInput("opam-repositories", { required: false, trimWhitespace: true }));
 const platform = getPlatform();
 const defaultRepository = platform !== "win32" /* Platform.Win32 */
     ? "https://github.com/ocaml/opam-repository.git"
diff --git a/dist/post/index.js b/dist/post/index.js
index 42a548a2..8b6a4b98 100644
--- a/dist/post/index.js
+++ b/dist/post/index.js
@@ -91362,32 +91362,39 @@ const CYGWIN_ROOT = external_path_.join("D:", "cygwin");
 const CYGWIN_ROOT_BIN = external_path_.join(CYGWIN_ROOT, "bin");
 const CYGWIN_ROOT_WRAPPERBIN = external_path_.join(CYGWIN_ROOT, "wrapperbin");
 const constants_CACHE_PREFIX = lib_core.getInput("cache-prefix", {
+    required: false,
     trimWhitespace: true,
 });
 const constants_GITHUB_TOKEN = lib_core.getInput("github-token", {
+    required: false,
     trimWhitespace: true,
 });
 const DUNE_CACHE = lib_core.getBooleanInput("dune-cache", {
+    required: false,
     trimWhitespace: true,
 });
 const constants_OCAML_COMPILER = lib_core.getInput("ocaml-compiler", {
+    required: true,
     trimWhitespace: true,
 });
 const OPAM_DEPEXT = lib_core.getBooleanInput("opam-depext", {
+    required: false,
     trimWhitespace: true,
 });
-const OPAM_DEPEXT_FLAGS = lib_core.getInput("opam-depext-flags", { trimWhitespace: true })
+const OPAM_DEPEXT_FLAGS = lib_core.getInput("opam-depext-flags", { required: false, trimWhitespace: true })
     .split(",")
     .map((f) => f.trim())
     .filter((f) => f.length > 0);
-const OPAM_DISABLE_SANDBOXING = lib_core.getBooleanInput("opam-disable-sandboxing", { trimWhitespace: true });
+const OPAM_DISABLE_SANDBOXING = lib_core.getBooleanInput("opam-disable-sandboxing", { required: false, trimWhitespace: true });
 const OPAM_LOCAL_PACKAGES = lib_core.getInput("opam-local-packages", {
+    required: false,
     trimWhitespace: true,
 });
 const OPAM_PIN = lib_core.getBooleanInput("opam-pin", {
+    required: false,
     trimWhitespace: true,
 });
-const repositories_yaml = dist/* parse */.Qc(lib_core.getInput("opam-repositories", { trimWhitespace: true }));
+const repositories_yaml = dist/* parse */.Qc(lib_core.getInput("opam-repositories", { required: false, trimWhitespace: true }));
 const platform = system_getPlatform();
 const defaultRepository = platform !== "win32" /* Platform.Win32 */
     ? "https://github.com/ocaml/opam-repository.git"
diff --git a/src/setup-ocaml/constants.ts b/src/setup-ocaml/constants.ts
index 358ea852..9c52691a 100644
--- a/src/setup-ocaml/constants.ts
+++ b/src/setup-ocaml/constants.ts
@@ -22,46 +22,53 @@ export const CYGWIN_ROOT_BIN = path.join(CYGWIN_ROOT, "bin");
 export const CYGWIN_ROOT_WRAPPERBIN = path.join(CYGWIN_ROOT, "wrapperbin");
 
 export const CACHE_PREFIX = core.getInput("cache-prefix", {
+  required: false,
   trimWhitespace: true,
 });
 
 export const GITHUB_TOKEN = core.getInput("github-token", {
+  required: false,
   trimWhitespace: true,
 });
 
 export const DUNE_CACHE = core.getBooleanInput("dune-cache", {
+  required: false,
   trimWhitespace: true,
 });
 
 export const OCAML_COMPILER = core.getInput("ocaml-compiler", {
+  required: true,
   trimWhitespace: true,
 });
 
 export const OPAM_DEPEXT = core.getBooleanInput("opam-depext", {
+  required: false,
   trimWhitespace: true,
 });
 
 export const OPAM_DEPEXT_FLAGS = core
-  .getInput("opam-depext-flags", { trimWhitespace: true })
+  .getInput("opam-depext-flags", { required: false, trimWhitespace: true })
   .split(",")
   .map((f) => f.trim())
   .filter((f) => f.length > 0);
 
 export const OPAM_DISABLE_SANDBOXING = core.getBooleanInput(
   "opam-disable-sandboxing",
-  { trimWhitespace: true }
+  { required: false, trimWhitespace: true }
 );
 
 export const OPAM_LOCAL_PACKAGES = core.getInput("opam-local-packages", {
+  required: false,
   trimWhitespace: true,
 });
 
 export const OPAM_PIN = core.getBooleanInput("opam-pin", {
+  required: false,
   trimWhitespace: true,
 });
 
 const repositories_yaml = yaml.parse(
-  core.getInput("opam-repositories", { trimWhitespace: true })
+  core.getInput("opam-repositories", { required: false, trimWhitespace: true })
 ) as Record<string, string> | null;
 
 const platform = getPlatform();