diff --git a/src/cloudabi/mod.rs b/src/cloudabi/mod.rs
index 0d8696210947e60d7988e466ac6f785c1ac2bb56..228740c2811a79314575f082bef2afa6c8c3689a 100644
--- a/src/cloudabi/mod.rs
+++ b/src/cloudabi/mod.rs
@@ -136,6 +136,7 @@ extern {
     pub fn isspace(c: c_int) -> c_int;
     pub fn isupper(c: c_int) -> c_int;
     pub fn isxdigit(c: c_int) -> c_int;
+    pub fn isblank(c: c_int) -> c_int;
     pub fn tolower(c: c_int) -> c_int;
     pub fn toupper(c: c_int) -> c_int;
     pub fn fopen(filename: *const c_char, mode: *const c_char) -> *mut FILE;
diff --git a/src/fuchsia/mod.rs b/src/fuchsia/mod.rs
index 0756866f51e296de46892d832464da1948e9e935..9136f36baca4e0720c2be766c6181c41a5330012 100644
--- a/src/fuchsia/mod.rs
+++ b/src/fuchsia/mod.rs
@@ -3282,6 +3282,7 @@ extern {
     pub fn isspace(c: c_int) -> c_int;
     pub fn isupper(c: c_int) -> c_int;
     pub fn isxdigit(c: c_int) -> c_int;
+    pub fn isblank(c: c_int) -> c_int;
     pub fn tolower(c: c_int) -> c_int;
     pub fn toupper(c: c_int) -> c_int;
     pub fn fopen(filename: *const c_char, mode: *const c_char) -> *mut FILE;
diff --git a/src/unix/mod.rs b/src/unix/mod.rs
index 721d241164a1d95a7e207b5d9087aa2e78557f8f..8ed1040b087c3c4f51cfea75f8afaa4e41ce2f92 100644
--- a/src/unix/mod.rs
+++ b/src/unix/mod.rs
@@ -379,6 +379,7 @@ extern {
     pub fn isspace(c: c_int) -> c_int;
     pub fn isupper(c: c_int) -> c_int;
     pub fn isxdigit(c: c_int) -> c_int;
+    pub fn isblank(c: c_int) -> c_int;
     pub fn tolower(c: c_int) -> c_int;
     pub fn toupper(c: c_int) -> c_int;
     #[cfg_attr(
diff --git a/src/vxworks/mod.rs b/src/vxworks/mod.rs
index dd6e6f1cb57333d13f55c27d68addf74c6ddfa92..92c5d6326825c538a0bff8ee24761a638eab67f7 100755
--- a/src/vxworks/mod.rs
+++ b/src/vxworks/mod.rs
@@ -962,6 +962,7 @@ extern {
     pub fn isspace(c: c_int) -> c_int;
     pub fn isupper(c: c_int) -> c_int;
     pub fn isxdigit(c: c_int) -> c_int;
+    pub fn isblank(c: c_int) -> c_int;
     pub fn tolower(c: c_int) -> c_int;
     pub fn toupper(c: c_int) -> c_int;
     pub fn fopen(filename: *const c_char, mode: *const c_char) -> *mut FILE;
diff --git a/src/windows/mod.rs b/src/windows/mod.rs
index be28b70f5664f65a868fc6d4cd414f3528a8988e..0d549a0aabb4fff33111f546395adc55a8c18377 100644
--- a/src/windows/mod.rs
+++ b/src/windows/mod.rs
@@ -222,6 +222,7 @@ extern {
     pub fn isspace(c: c_int) -> c_int;
     pub fn isupper(c: c_int) -> c_int;
     pub fn isxdigit(c: c_int) -> c_int;
+    pub fn isblank(c: c_int) -> c_int;
     pub fn tolower(c: c_int) -> c_int;
     pub fn toupper(c: c_int) -> c_int;
     pub fn fopen(filename: *const c_char, mode: *const c_char) -> *mut FILE;