diff --git a/scripts/run-real-verification.mjs b/scripts/run-real-verification.mjs
index af455b3..2ee886c 100644
--- a/scripts/run-real-verification.mjs
+++ b/scripts/run-real-verification.mjs
@@ -21,6 +21,11 @@ const chromeTests = Object.keys(scripts)
 const wasmBuilds = process.env.CI_REAL_REBUILD_WASM === '1'
   ? ['fetch:freecad-source', 'build:occt-history', 'build:planegcs']
   : []
+if (wasmBuilds.length > 0) {
+  for (const variable of ['OCCT_SOURCE_DIR', 'EMSDK']) {
+    if (!process.env[variable]) throw new Error(`CI_REAL_REBUILD_WASM=1 requires ${variable} to be configured.`)
+  }
+}
 
 const lanes = {
   chrome: [