diff --git a/doc/modbus_set_debug.txt b/doc/modbus_set_debug.txt
index 9e6a2e9..7621e03 100644
--- a/doc/modbus_set_debug.txt
+++ b/doc/modbus_set_debug.txt
@@ -8,15 +8,16 @@ modbus_set_debug - set debug flag of the context
 
 SYNOPSIS
 --------
-*int modbus_set_debug(modbus_t *'ctx', int 'boolean');*
+*int modbus_set_debug(modbus_t *'ctx', int 'flag');*
 
 
 DESCRIPTION
 -----------
 The _modbus_set_debug()_ function shall set the debug flag of the *modbus_t*
-context by using the argument 'boolean'. When the 'boolean' value is set to
-'TRUE', many verbose messages are displayed on stdout and stderr. For example,
-this flag is useful to display the bytes of the Modbus messages.
+context by using the argument 'flag'. By default, the boolean flag is set to
+'FALSE'. When the 'flag' value is set to 'TRUE', many verbose messages are
+displayed on stdout and stderr. For example, this flag is useful to display the
+bytes of the Modbus messages.
 
 [verse]
 ___________________
diff --git a/src/modbus.c b/src/modbus.c
index e8cf909..7dcc50e 100644
--- a/src/modbus.c
+++ b/src/modbus.c
@@ -1667,14 +1667,14 @@ void modbus_free(modbus_t *ctx)
     ctx->backend->free(ctx);
 }
 
-int modbus_set_debug(modbus_t *ctx, int boolean)
+int modbus_set_debug(modbus_t *ctx, int flag)
 {
     if (ctx == NULL) {
         errno = EINVAL;
         return -1;
     }
 
-    ctx->debug = boolean;
+    ctx->debug = flag;
     return 0;
 }
 
diff --git a/src/modbus.h b/src/modbus.h
index c5eb1ff..8d245a8 100644
--- a/src/modbus.h
+++ b/src/modbus.h
@@ -173,7 +173,7 @@ EXPORT void modbus_close(modbus_t *ctx);
 EXPORT void modbus_free(modbus_t *ctx);
 
 EXPORT int modbus_flush(modbus_t *ctx);
-EXPORT int modbus_set_debug(modbus_t *ctx, int boolean);
+EXPORT int modbus_set_debug(modbus_t *ctx, int flag);
 
 EXPORT const char *modbus_strerror(int errnum);