diff --git a/libc/bionic/wchar.cpp b/libc/bionic/wchar.cpp
index 8d5645857..8367817ec 100644
--- a/libc/bionic/wchar.cpp
+++ b/libc/bionic/wchar.cpp
@@ -97,6 +97,7 @@ int swscanf(const wchar_t* /*s*/, const wchar_t* /*format*/, ... ) {
 
 int iswalnum(wint_t wc) { return isalnum(wc); }
 int iswalpha(wint_t wc) { return isalpha(wc); }
+int iswblank(wint_t wc) { return isblank(wc); }
 int iswcntrl(wint_t wc) { return iscntrl(wc); }
 int iswdigit(wint_t wc) { return isdigit(wc); }
 int iswgraph(wint_t wc) { return isgraph(wc); }
diff --git a/libc/include/wchar.h b/libc/include/wchar.h
index 89c6fb603..04818b953 100644
--- a/libc/include/wchar.h
+++ b/libc/include/wchar.h
@@ -70,6 +70,7 @@ extern int               fwprintf(FILE *, const wchar_t *, ...);
 extern int               fwscanf(FILE *, const wchar_t *, ...);
 extern int               iswalnum(wint_t);
 extern int               iswalpha(wint_t);
+extern int               iswblank(wint_t);
 extern int               iswcntrl(wint_t);
 extern int               iswdigit(wint_t);
 extern int               iswgraph(wint_t);