diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e4aa06c..60d6eb3 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -51,3 +51,6 @@ jobs:
         run: |
           cd prove
           alr exec -- gnatprove -P ../cobs.gpr
+        # Skip on Windows due to broken toolchain/environment which causes
+        # all proof checks to fail (except initialization and termination).
+        if: matrix.os != 'windows-latest'
diff --git a/cobs.gpr b/cobs.gpr
index 31edf8c..66b9a6f 100644
--- a/cobs.gpr
+++ b/cobs.gpr
@@ -36,7 +36,8 @@ project Cobs is
                                       "--timeout=60",
                                       "--memlimit=0",
                                       "--steps=15000",
-                                      "--report=statistics");
+                                      "--report=statistics",
+                                      "--checks-as-errors");
    end Prove;
 
 end Cobs;