diff --git a/src/script/interpreter.h b/src/script/interpreter.h
--- a/src/script/interpreter.h
+++ b/src/script/interpreter.h
@@ -106,6 +106,10 @@
     // Do we accept activate replay protection using a different fork id.
     //
     SCRIPT_ENABLE_REPLAY_PROTECTION = (1U << 17),
+
+    // Is OP_CHECKDATASIG and variant are enabled.
+    //
+    SCRIPT_ENABLE_CHECKDATASIG = (1U << 18),
 };
 
 bool CheckSignatureEncoding(const std::vector<uint8_t> &vchSig, uint32_t flags,
diff --git a/src/script/interpreter.cpp b/src/script/interpreter.cpp
--- a/src/script/interpreter.cpp
+++ b/src/script/interpreter.cpp
@@ -140,7 +140,7 @@
 
     // Verify that the length of the signature matches the sum of the length
     // of the elements.
-    if ((size_t)(lenR + lenS + 7) != sig.size()) return false;
+    if (size_t(lenR + lenS + 7) != sig.size()) return false;
 
     // Check whether the R element is an integer.
     if (sig[2] != 0x02) return false;
diff --git a/src/test/checkdatasig_tests.cpp b/src/test/checkdatasig_tests.cpp
--- a/src/test/checkdatasig_tests.cpp
+++ b/src/test/checkdatasig_tests.cpp
@@ -28,10 +28,19 @@
     BaseSignatureChecker sigchecker;
 
     for (uint32_t flags : flagset) {
-        // Make sure that opcodes are disabled.
+        // The opcode are not implemented yet, so we get a bad opcode error when
+        // passing the activation flag.
         ScriptError err = SCRIPT_ERR_OK;
         stacktype stack{original_stack};
-        bool r = EvalScript(stack, script, flags, sigchecker, &err);
+        bool r = EvalScript(stack, script, flags | SCRIPT_ENABLE_CHECKDATASIG,
+                            sigchecker, &err);
+        BOOST_CHECK(!r);
+        BOOST_CHECK_EQUAL(err, SCRIPT_ERR_BAD_OPCODE);
+
+        // Make sure that we get a bad opcode when the activation flag is not
+        // passed.
+        stack = original_stack;
+        r = EvalScript(stack, script, flags, sigchecker, &err);
         BOOST_CHECK(!r);
         BOOST_CHECK_EQUAL(err, SCRIPT_ERR_BAD_OPCODE);
     }
diff --git a/src/test/data/script_tests.json b/src/test/data/script_tests.json
--- a/src/test/data/script_tests.json
+++ b/src/test/data/script_tests.json
@@ -241,7 +241,9 @@
  "Discouraged NOPs are allowed if not executed"],
 
 ["0", "IF CHECKDATASIG ELSE 1 ENDIF", "P2SH,STRICTENC", "OK"],
+["0", "IF CHECKDATASIG ELSE 1 ENDIF", "P2SH,STRICTENC,CHECKDATASIG", "OK"],
 ["0", "IF CHECKDATASIGVERIFY ELSE 1 ENDIF", "P2SH,STRICTENC", "OK"],
+["0", "IF CHECKDATASIGVERIFY ELSE 1 ENDIF", "P2SH,STRICTENC,CHECKDATASIG", "OK"],
 ["0", "IF 0xbc ELSE 1 ENDIF", "P2SH,STRICTENC", "OK", "opcodes >= FIRST_UNDEFINED_OP_VALUE invalid if executed"],
 ["0", "IF 0xbd ELSE 1 ENDIF", "P2SH,STRICTENC", "OK"],
 ["0", "IF 0xbe ELSE 1 ENDIF", "P2SH,STRICTENC", "OK"],
@@ -1067,7 +1069,9 @@
 
 ["0x50","1", "P2SH,STRICTENC", "BAD_OPCODE", "opcode 0x50 is reserved"],
 ["1", "IF CHECKDATASIG ELSE 1 ENDIF", "P2SH,STRICTENC", "BAD_OPCODE"],
+["1", "IF CHECKDATASIG ELSE 1 ENDIF", "P2SH,STRICTENC,CHECKDATASIG", "BAD_OPCODE"],
 ["1", "IF CHECKDATASIGVERIFY ELSE 1 ENDIF", "P2SH,STRICTENC", "BAD_OPCODE"],
+["1", "IF CHECKDATASIGVERIFY ELSE 1 ENDIF", "P2SH,STRICTENC,CHECKDATASIG", "BAD_OPCODE"],
 ["1", "IF 0xbc ELSE 1 ENDIF", "P2SH,STRICTENC", "BAD_OPCODE", "opcodes >= FIRST_UNDEFINED_OP_VALUE invalid if executed"],
 ["1", "IF 0xbd ELSE 1 ENDIF", "P2SH,STRICTENC", "BAD_OPCODE"],
 ["1", "IF 0xbe ELSE 1 ENDIF", "P2SH,STRICTENC", "BAD_OPCODE"],
diff --git a/src/test/scriptflags.cpp b/src/test/scriptflags.cpp
--- a/src/test/scriptflags.cpp
+++ b/src/test/scriptflags.cpp
@@ -31,6 +31,7 @@
     {"COMPRESSED_PUBKEYTYPE", SCRIPT_VERIFY_COMPRESSED_PUBKEYTYPE},
     {"SIGHASH_FORKID", SCRIPT_ENABLE_SIGHASH_FORKID},
     {"REPLAY_PROTECTION", SCRIPT_ENABLE_REPLAY_PROTECTION},
+    {"CHECKDATASIG", SCRIPT_ENABLE_CHECKDATASIG},
 };
 
 uint32_t ParseScriptFlags(std::string strFlags) {