diff --git a/ChangeLog.md b/ChangeLog.md
index dfc14c3..8c4585a 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -8,6 +8,7 @@
 
 - Fix compilation for compilers other than gcc, clang, msvc.
 - Add build with tcc to CI.
+- Rewrote `mk_wcwidth` function.
 
 ## v0.3.1
 
diff --git a/lib/fort.c b/lib/fort.c
index 1fefa4c..846e503 100644
--- a/lib/fort.c
+++ b/lib/fort.c
@@ -7180,8 +7180,8 @@ void vector_clear(f_vector_t *vector)
 
 
 struct interval {
-    wchar_t first;
-    wchar_t last;
+    int32_t first;
+    int32_t last;
 };
 
 /* auxiliary function for binary search in interval table */
@@ -7237,7 +7237,7 @@ static int bisearch(wchar_t ucs, const struct interval *table, int max)
  * in ISO 10646.
  */
 
-static int mk_wcwidth(wchar_t ucs)
+static int mk_wcwidth(wchar_t wcs)
 {
     /* sorted list of non-overlapping intervals of non-spacing characters */
     /* generated by "uniset +cat=Me +cat=Mn +cat=Cf -00AD +1160-11FF +200B c" */
@@ -7292,6 +7292,14 @@ static int mk_wcwidth(wchar_t ucs)
         { 0xE0100, 0xE01EF }
     };
 
+    /* We convert wchar_t to int32_t to avoid compiler warnings
+     * about implicit integer conversions
+     * https://github.com/seleznevae/libfort/issues/20
+     *
+     * note: didn't test if we can do it
+     */
+    int32_t ucs = (int32_t)wcs;
+
     /* test for 8-bit control characters */
     if (ucs == 0)
         return 0;
diff --git a/src/wcwidth.c b/src/wcwidth.c
index f97b879..6bdf790 100644
--- a/src/wcwidth.c
+++ b/src/wcwidth.c
@@ -65,8 +65,8 @@
 
 
 struct interval {
-    wchar_t first;
-    wchar_t last;
+    int32_t first;
+    int32_t last;
 };
 
 /* auxiliary function for binary search in interval table */
@@ -122,7 +122,7 @@ static int bisearch(wchar_t ucs, const struct interval *table, int max)
  * in ISO 10646.
  */
 
-static int mk_wcwidth(wchar_t ucs)
+static int mk_wcwidth(wchar_t wcs)
 {
     /* sorted list of non-overlapping intervals of non-spacing characters */
     /* generated by "uniset +cat=Me +cat=Mn +cat=Cf -00AD +1160-11FF +200B c" */
@@ -177,6 +177,14 @@ static int mk_wcwidth(wchar_t ucs)
         { 0xE0100, 0xE01EF }
     };
 
+    /* We convert wchar_t to int32_t to avoid compiler warnings
+     * about implicit integer conversions
+     * https://github.com/seleznevae/libfort/issues/20
+     *
+     * note: didn't test if we can do it
+     */
+    int32_t ucs = (int32_t)wcs;
+
     /* test for 8-bit control characters */
     if (ucs == 0)
         return 0;