diff --git a/src/cloudabi/mod.rs b/src/cloudabi/mod.rs
index 551ef0b5297eb610e32d93d3731d0c8d1e7e9963..b3065d7237383978f8a722e66db9b09bf9b2b689 100644
--- a/src/cloudabi/mod.rs
+++ b/src/cloudabi/mod.rs
@@ -140,6 +140,7 @@ extern "C" {
     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 86505281d0594db8978e0bcdc992d0cfa9cae706..5d302aaf8840dbb6c8ef6ac81394482cabe8c923 100644
--- a/src/fuchsia/mod.rs
+++ b/src/fuchsia/mod.rs
@@ -3293,6 +3293,7 @@ extern "C" {
     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 5fc0f9bf36f5f20d419bc3c8e33f1f0e984150c1..8d78cea7269d372304b1189ea2af8e52915ecf6e 100644
--- a/src/unix/mod.rs
+++ b/src/unix/mod.rs
@@ -385,6 +385,7 @@ extern "C" {
     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 f96afc790448d289113c26d62a550db8b1b1143c..37a8c2c56ffd255dd3ecfc7f572f7a920424df9c 100755
--- a/src/vxworks/mod.rs
+++ b/src/vxworks/mod.rs
@@ -962,6 +962,7 @@ extern "C" {
     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 819b82c404c469d38a3e5c20d2a11ffa2aa2ede1..ba80e0ca0f6c8caec667f9e330fc92d4ff296788 100644
--- a/src/windows/mod.rs
+++ b/src/windows/mod.rs
@@ -228,6 +228,7 @@ extern "C" {
     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;