diff --git a/src/avalanche/processor.cpp b/src/avalanche/processor.cpp
--- a/src/avalanche/processor.cpp
+++ b/src/avalanche/processor.cpp
@@ -193,7 +193,7 @@
     if (argsman.IsArgSet("-avasessionkey")) {
         sessionKey = DecodeSecret(argsman.GetArg("-avasessionkey", ""));
         if (!sessionKey.IsValid()) {
-            error = _("the avalanche session key is invalid");
+            error = _("The avalanche session key is invalid.");
             return nullptr;
         }
     } else {
@@ -204,13 +204,13 @@
     if (argsman.IsArgSet("-avaproof")) {
         if (!argsman.IsArgSet("-avamasterkey")) {
             error = _(
-                "the avalanche master key is missing for the avalanche proof");
+                "The avalanche master key is missing for the avalanche proof.");
             return nullptr;
         }
 
         masterKey = DecodeSecret(argsman.GetArg("-avamasterkey", ""));
         if (!masterKey.IsValid()) {
-            error = _("the avalanche master key is invalid");
+            error = _("The avalanche master key is invalid.");
             return nullptr;
         }
 
@@ -226,25 +226,25 @@
         if (!peerData->proof->verify(proof_state)) {
             switch (proof_state.GetResult()) {
                 case ProofValidationResult::NO_STAKE:
-                    error = _("the avalanche proof has no stake");
+                    error = _("The avalanche proof has no stake.");
                     return nullptr;
                 case ProofValidationResult::DUST_THRESOLD:
-                    error = _("the avalanche proof stake is too low");
+                    error = _("The avalanche proof stake is too low.");
                     return nullptr;
                 case ProofValidationResult::DUPLICATE_STAKE:
-                    error = _("the avalanche proof has duplicated stake");
+                    error = _("The avalanche proof has duplicated stake.");
                     return nullptr;
                 case ProofValidationResult::INVALID_SIGNATURE:
                     error =
-                        _("the avalanche proof has invalid stake signatures");
+                        _("The avalanche proof has invalid stake signatures.");
                     return nullptr;
                 case ProofValidationResult::TOO_MANY_UTXOS:
                     error = strprintf(
-                        _("the avalanche proof has too many utxos (max: %u)"),
+                        _("The avalanche proof has too many utxos (max: %u)."),
                         AVALANCHE_MAX_PROOF_STAKES);
                     return nullptr;
                 default:
-                    error = _("the avalanche proof is invalid");
+                    error = _("The avalanche proof is invalid.");
                     return nullptr;
             }
         }
diff --git a/test/functional/abc_rpc_avalancheproof.py b/test/functional/abc_rpc_avalancheproof.py
--- a/test/functional/abc_rpc_avalancheproof.py
+++ b/test/functional/abc_rpc_avalancheproof.py
@@ -334,14 +334,14 @@
             self.extra_args[0] + [
                 "-avasessionkey=0",
             ],
-            expected_msg="Error: the avalanche session key is invalid",
+            expected_msg="Error: The avalanche session key is invalid.",
         )
 
         node.assert_start_raises_init_error(
             self.extra_args[0] + [
                 "-avaproof={}".format(proof),
             ],
-            expected_msg="Error: the avalanche master key is missing for the avalanche proof",
+            expected_msg="Error: The avalanche master key is missing for the avalanche proof.",
         )
 
         node.assert_start_raises_init_error(
@@ -349,7 +349,7 @@
                 "-avaproof={}".format(proof),
                 "-avamasterkey=0",
             ],
-            expected_msg="Error: the avalanche master key is invalid",
+            expected_msg="Error: The avalanche master key is invalid.",
         )
 
         def check_proof_init_error(proof, message):
@@ -362,15 +362,15 @@
             )
 
         check_proof_init_error(no_stake,
-                               "the avalanche proof has no stake")
+                               "The avalanche proof has no stake.")
         check_proof_init_error(dust,
-                               "the avalanche proof stake is too low")
+                               "The avalanche proof stake is too low.")
         check_proof_init_error(dust2,
-                               "the avalanche proof stake is too low")
+                               "The avalanche proof stake is too low.")
         check_proof_init_error(duplicate_stake,
-                               "the avalanche proof has duplicated stake")
+                               "The avalanche proof has duplicated stake.")
         check_proof_init_error(bad_sig,
-                               "the avalanche proof has invalid stake signatures")
+                               "The avalanche proof has invalid stake signatures.")
         if self.is_wallet_compiled():
             # The too many utxos case creates a proof which is that large that it
             # cannot fit on the command line
@@ -379,7 +379,7 @@
                 self.extra_args[0] + [
                     "-avamasterkey=cND2ZvtabDbJ1gucx9GWH6XT9kgTAqfb6cotPt5Q5CyxVDhid2EN",
                 ],
-                expected_msg="Error: the avalanche proof has too many utxos",
+                expected_msg="Error: The avalanche proof has too many utxos.",
                 match=ErrorMatch.PARTIAL_REGEX,
             )