diff --git a/Modules/_json.c b/Modules/_json.c
index 95c658c..40c2ced 100644
--- a/Modules/_json.c
+++ b/Modules/_json.c
@@ -246,6 +246,7 @@
         }
     }
     output[chars++] = '"';
+    assert(_PyUnicode_CheckConsistency(rval, 1));
     return rval;
 }
 
diff --git a/Modules/md5module.c b/Modules/md5module.c
index 86f602e..ee44c48 100644
--- a/Modules/md5module.c
+++ b/Modules/md5module.c
@@ -397,6 +397,7 @@
         c = (digest[i] & 0xf);
         hex_digest[j++] = Py_hexdigits[c];
     }
+    assert(_PyUnicode_CheckConsistency(retval, 1));
     return retval;
 }
 
diff --git a/Modules/sha1module.c b/Modules/sha1module.c
index 30e5c50..daea887 100644
--- a/Modules/sha1module.c
+++ b/Modules/sha1module.c
@@ -373,6 +373,7 @@
         c = (digest[i] & 0xf);
         hex_digest[j++] = Py_hexdigits[c];
     }
+    assert(_PyUnicode_CheckConsistency(retval, 1));
     return retval;
 }
 
diff --git a/Modules/sha256module.c b/Modules/sha256module.c
index f1ef329..76d91af 100644
--- a/Modules/sha256module.c
+++ b/Modules/sha256module.c
@@ -466,6 +466,7 @@
         c = (digest[i] & 0xf);
         hex_digest[j++] = Py_hexdigits[c];
     }
+    assert(_PyUnicode_CheckConsistency(retval, 1));
     return retval;
 }
 
diff --git a/Modules/sha512module.c b/Modules/sha512module.c
index 4f5a113..88f8a64 100644
--- a/Modules/sha512module.c
+++ b/Modules/sha512module.c
@@ -532,6 +532,7 @@
         c = (digest[i] & 0xf);
         hex_digest[j++] = Py_hexdigits[c];
     }
+    assert(_PyUnicode_CheckConsistency(retval, 1));
     return retval;
 }