Index: generic/tls.c
==================================================================
--- generic/tls.c
+++ generic/tls.c
@@ -419,11 +419,11 @@
  *	  to a string describing the SSL negotiation failure reason
  *
  *-------------------------------------------------------------------
  */
 void
-Tls_Error(State *statePtr, char *msg) {
+Tls_Error(State *statePtr, const char *msg) {
     Tcl_Interp *interp	= statePtr->interp;
     Tcl_Obj *cmdPtr, *listPtr;
     unsigned long err;
     statePtr->err = msg;
 

Index: generic/tlsIO.c
==================================================================
--- generic/tlsIO.c
+++ generic/tlsIO.c
@@ -238,32 +238,32 @@
 		dprintf("I/O error occurred (errno = %lu)", (unsigned long) Tcl_GetErrno());
 		*errorCodePtr = Tcl_GetErrno();
 		if (*errorCodePtr == ECONNRESET) {
 		    *errorCodePtr = ECONNABORTED;
 		}
-		Tls_Error(statePtr, (char *) Tcl_ErrnoMsg(*errorCodePtr));
+		Tls_Error(statePtr, Tcl_ErrnoMsg(*errorCodePtr));
 
 	    } else {
 		dprintf("I/O error occurred (backingError = %lu)", backingError);
 		*errorCodePtr = Tcl_GetErrno();
 		if (*errorCodePtr == ECONNRESET) {
 		    *errorCodePtr = ECONNABORTED;
 		}
-		Tls_Error(statePtr, (char *) ERR_reason_error_string(backingError));
+		Tls_Error(statePtr, ERR_reason_error_string(backingError));
 	    }
 
 	    statePtr->flags |= TLS_TCL_HANDSHAKE_FAILED;
 	    return -1;
 
 	case SSL_ERROR_SSL:
 	    /* A non-recoverable, fatal error in the SSL library occurred, usually a protocol error */
 	    dprintf("SSL_ERROR_SSL: Got permanent fatal SSL error, aborting immediately");
 	    if (SSL_get_verify_result(statePtr->ssl) != X509_V_OK) {
-		Tls_Error(statePtr, (char *) X509_verify_cert_error_string(SSL_get_verify_result(statePtr->ssl)));
+		Tls_Error(statePtr, X509_verify_cert_error_string(SSL_get_verify_result(statePtr->ssl)));
 	    }
 	    if (backingError != 0) {
-		Tls_Error(statePtr, (char *) ERR_reason_error_string(backingError));
+		Tls_Error(statePtr, ERR_reason_error_string(backingError));
 	    }
 	    statePtr->flags |= TLS_TCL_HANDSHAKE_FAILED;
 	    *errorCodePtr = ECONNABORTED;
 	    return -1;
 	default:
@@ -373,13 +373,13 @@
 
 	case SSL_ERROR_SSL:
 	    /* A non-recoverable, fatal error in the SSL library occurred, usually a protocol error */
 	    dprintf("SSL error, indicating that the connection has been aborted");
 	    if (backingError != 0) {
-		Tls_Error(statePtr, (char *) ERR_reason_error_string(backingError));
+		Tls_Error(statePtr, ERR_reason_error_string(backingError));
 	    } else if (SSL_get_verify_result(statePtr->ssl) != X509_V_OK) {
-		Tls_Error(statePtr, (char *) X509_verify_cert_error_string(SSL_get_verify_result(statePtr->ssl)));
+		Tls_Error(statePtr, X509_verify_cert_error_string(SSL_get_verify_result(statePtr->ssl)));
 	    } else {
 		Tls_Error(statePtr, "Unknown SSL error");
 	    }
 	    *errorCodePtr = ECONNABORTED;
 	    bytesRead = -1;
@@ -407,17 +407,17 @@
 
 	    } else if (backingError == 0 && bytesRead == -1) {
 		dprintf("I/O error occurred (errno = %lu)", (unsigned long) Tcl_GetErrno());
 		*errorCodePtr = Tcl_GetErrno();
 		bytesRead = -1;
-		Tls_Error(statePtr, (char *) Tcl_ErrnoMsg(*errorCodePtr));
+		Tls_Error(statePtr, Tcl_ErrnoMsg(*errorCodePtr));
 
 	    } else {
 		dprintf("I/O error occurred (backingError = %lu)", backingError);
 		*errorCodePtr = Tcl_GetErrno();
 		bytesRead = -1;
-		Tls_Error(statePtr, (char *) ERR_reason_error_string(backingError));
+		Tls_Error(statePtr, ERR_reason_error_string(backingError));
 	    }
 	    break;
 
 	case SSL_ERROR_ZERO_RETURN:
 	    dprintf("Got SSL_ERROR_ZERO_RETURN, this means an EOF has been reached");
@@ -580,27 +580,27 @@
 
 	    } else if (backingError == 0 && written == -1) {
 		dprintf("I/O error occurred (errno = %lu)", (unsigned long) Tcl_GetErrno());
 		*errorCodePtr = Tcl_GetErrno();
 		written = -1;
-		Tls_Error(statePtr, (char *) Tcl_ErrnoMsg(*errorCodePtr));
+		Tls_Error(statePtr, Tcl_ErrnoMsg(*errorCodePtr));
 
 	    } else {
 		dprintf("I/O error occurred (backingError = %lu)", backingError);
 		*errorCodePtr = Tcl_GetErrno();
 		written = -1;
-		Tls_Error(statePtr, (char *) ERR_reason_error_string(backingError));
+		Tls_Error(statePtr, ERR_reason_error_string(backingError));
 	    }
 	    break;
 
 	case SSL_ERROR_SSL:
 	    /* A non-recoverable, fatal error in the SSL library occurred, usually a protocol error */
 	    dprintf("SSL error, indicating that the connection has been aborted");
 	    if (backingError != 0) {
-		Tls_Error(statePtr, (char *) ERR_reason_error_string(backingError));
+		Tls_Error(statePtr, ERR_reason_error_string(backingError));
 	    } else if (SSL_get_verify_result(statePtr->ssl) != X509_V_OK) {
-		Tls_Error(statePtr, (char *) X509_verify_cert_error_string(SSL_get_verify_result(statePtr->ssl)));
+		Tls_Error(statePtr, X509_verify_cert_error_string(SSL_get_verify_result(statePtr->ssl)));
 	    } else {
 		Tls_Error(statePtr, "Unknown SSL error");
 	    }
 	    *errorCodePtr = ECONNABORTED;
 	    written = -1;

Index: generic/tlsInt.h
==================================================================
--- generic/tlsInt.h
+++ generic/tlsInt.h
@@ -203,11 +203,11 @@
 const Tcl_ChannelType *Tls_ChannelType(void);
 Tcl_Channel     Tls_GetParent(State *statePtr, int maskFlags);
 
 Tcl_Obj        *Tls_NewX509Obj(Tcl_Interp *interp, X509 *cert);
 Tcl_Obj        *Tls_NewCAObj(Tcl_Interp *interp, const SSL *ssl, int peer);
-void            Tls_Error(State *statePtr, char *msg);
+void            Tls_Error(State *statePtr, const char *msg);
 #if TCL_MAJOR_VERSION > 8
 void            Tls_Free(void *blockPtr);
 #else
 void            Tls_Free(char *blockPtr);
 #endif