diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3c6d58e..19db91f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.0)
 
-project(libfort VERSION 0.3.1)
+project(libfort VERSION 0.3.2)
 
 string(REGEX REPLACE "([0-9]+)\\.([0-9]+)\\.([0-9]+)"
     "\\1.\\2" libfort_SOVERSION
diff --git a/ChangeLog.md b/ChangeLog.md
index 8ecaa1b..7b3bbbd 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,9 @@
+## v0.3.2
+
+### Bug fixes
+
+- Fix undefined behavior due to incorrect usage of `isprint` function.
+
 ## v0.3.1
 
 ### Bug fixes
diff --git a/lib/fort.c b/lib/fort.c
index 9888e9e..d93b162 100644
--- a/lib/fort.c
+++ b/lib/fort.c
@@ -2582,7 +2582,6 @@ SOFTWARE.
 #include <assert.h>
 #include <string.h>
 #include <wchar.h>
-#include <ctype.h>
 
 /* #include "vector.h" */ /* Commented by amalgamation script */
 /* #include "fort_utils.h" */ /* Commented by amalgamation script */
@@ -5416,10 +5415,14 @@ int print_row_separator_impl(f_conv_context_t *cntx,
     size_t i = 0;
 
     /* If all chars are not printable, skip line separator */
-    if ((strlen(*L) == 0 || (strlen(*L) == 1 && !isprint(**L)))
-        && (strlen(*I) == 0 || (strlen(*I) == 1 && !isprint(**I)))
-        && (strlen(*IV) == 0 || (strlen(*IV) == 1 && !isprint(**IV)))
-        && (strlen(*R) == 0 || (strlen(*R) == 1 && !isprint(**R)))) {
+    /* NOTE: argument of `isprint` should be explicitly converted to
+     * unsigned char according to
+     * https://en.cppreference.com/w/c/string/byte/isprint
+     */
+    if ((strlen(*L) == 0 || (strlen(*L) == 1 && !isprint((unsigned char) **L)))
+        && (strlen(*I) == 0 || (strlen(*I) == 1 && !isprint((unsigned char) **I)))
+        && (strlen(*IV) == 0 || (strlen(*IV) == 1 && !isprint((unsigned char) **IV)))
+        && (strlen(*R) == 0 || (strlen(*R) == 1 && !isprint((unsigned char) **R)))) {
         status = 0;
         goto clear;
     }
diff --git a/lib/fort.h b/lib/fort.h
index a45a0e4..efda242 100644
--- a/lib/fort.h
+++ b/lib/fort.h
@@ -46,8 +46,8 @@ SOFTWARE.
 
 #define LIBFORT_MAJOR_VERSION 0
 #define LIBFORT_MINOR_VERSION 3
-#define LIBFORT_REVISION 0
-#define LIBFORT_VERSION_STR "0.3.0"
+#define LIBFORT_REVISION 2
+#define LIBFORT_VERSION_STR "0.3.2"
 
 
 /*****************************************************************************
diff --git a/src/fort.h b/src/fort.h
index a47ae64..efda242 100644
--- a/src/fort.h
+++ b/src/fort.h
@@ -46,8 +46,8 @@ SOFTWARE.
 
 #define LIBFORT_MAJOR_VERSION 0
 #define LIBFORT_MINOR_VERSION 3
-#define LIBFORT_REVISION 1
-#define LIBFORT_VERSION_STR "0.3.1"
+#define LIBFORT_REVISION 2
+#define LIBFORT_VERSION_STR "0.3.2"
 
 
 /*****************************************************************************
diff --git a/src/fort_impl.c b/src/fort_impl.c
index 446478e..8902658 100644
--- a/src/fort_impl.c
+++ b/src/fort_impl.c
@@ -31,7 +31,6 @@ SOFTWARE.
 #include <assert.h>
 #include <string.h>
 #include <wchar.h>
-#include <ctype.h>
 
 #include "vector.h"
 #include "fort_utils.h"
diff --git a/src/row.c b/src/row.c
index 0041213..84987c5 100644
--- a/src/row.c
+++ b/src/row.c
@@ -353,10 +353,14 @@ int print_row_separator_impl(f_conv_context_t *cntx,
     size_t i = 0;
 
     /* If all chars are not printable, skip line separator */
-    if ((strlen(*L) == 0 || (strlen(*L) == 1 && !isprint(**L)))
-        && (strlen(*I) == 0 || (strlen(*I) == 1 && !isprint(**I)))
-        && (strlen(*IV) == 0 || (strlen(*IV) == 1 && !isprint(**IV)))
-        && (strlen(*R) == 0 || (strlen(*R) == 1 && !isprint(**R)))) {
+    /* NOTE: argument of `isprint` should be explicitly converted to
+     * unsigned char according to
+     * https://en.cppreference.com/w/c/string/byte/isprint
+     */
+    if ((strlen(*L) == 0 || (strlen(*L) == 1 && !isprint((unsigned char) **L)))
+        && (strlen(*I) == 0 || (strlen(*I) == 1 && !isprint((unsigned char) **I)))
+        && (strlen(*IV) == 0 || (strlen(*IV) == 1 && !isprint((unsigned char) **IV)))
+        && (strlen(*R) == 0 || (strlen(*R) == 1 && !isprint((unsigned char) **R)))) {
         status = 0;
         goto clear;
     }