diff --git a/configure.ac b/configure.ac
index f01644b..b8589d0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -39,7 +39,7 @@ m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])])
 m4_ifdef([AM_PROG_AR], [AM_PROG_AR])
 
 # Enable more compiler warnings.
-CFLAGS="$CFLAGS -std=c99 -Wall -Wextra -pedantic -Wmissing-prototypes"
+CFLAGS="$CFLAGS -std=c99 -Wall -Wextra -pedantic -Wmissing-prototypes -Wshadow"
 
 # Checks for programs.
 AC_PROG_CC
diff --git a/libserialport_internal.h b/libserialport_internal.h
index 6a8c877..6a682cb 100644
--- a/libserialport_internal.h
+++ b/libserialport_internal.h
@@ -224,7 +224,7 @@ extern void (*sp_debug_handler)(const char *format, ...);
 #define TRACE(fmt, ...) DEBUG_FMT("%s(" fmt ") called", __func__, __VA_ARGS__)
 #define TRACE_VOID() DEBUG_FMT("%s() called", __func__)
 
-#define TRY(x) do { int ret = x; if (ret != SP_OK) RETURN_CODEVAL(ret); } while (0)
+#define TRY(x) do { int retval = x; if (retval != SP_OK) RETURN_CODEVAL(retval); } while (0)
 
 SP_PRIV struct sp_port **list_append(struct sp_port **list, const char *portname);