2 files changed, 12 insertions, 0 deletions
diff --git a/src/malloc.c b/src/malloc.c
index 6d1f220..9b45607 100644
--- a/src/malloc.c
+++ b/src/malloc.c
@@ -254,6 +254,8 @@ void* realloc(void* ptr, size_t size)
 
 /**
  * Free a memory allocation.
+ *  
+ * As a slibc extension, `errno` is guaranteed not to be set.
  * 
  * @etymology  (Free) allocated memory.
  * 
@@ -277,6 +279,8 @@ void free(void* ptr)
  * This function uses variadic arguments because there
  * there are multiple conflicting specifications for `cfree`.
  * 
+ * As a slibc extension, `errno` is guaranteed not to be set.
+ * 
  * @param  ptr  Pointer to the beginning of the memory allocation.
  *              The process may crash if it does not point to the
  *              beginning of a memory allocation on the heap.
diff --git a/src/slibc-alloc.c b/src/slibc-alloc.c
index 2f51603..f93a4b5 100644
--- a/src/slibc-alloc.c
+++ b/src/slibc-alloc.c
@@ -58,15 +58,19 @@
  * This function is identical to `free`, except it is guaranteed not to
  * override the memory segment with zeroes before freeing the allocation.
  * 
+ * `errno` is guaranteed not to be set.
+ * 
  * @param  segment  The memory segment to free.
  * 
  * @since  Always.
  */
 void fast_free(void* segment)
 {
+  int saved_errno = errno;
   if (segment == NULL)
     return;
   munmap(PURE_ALLOC(segment), PURE_SIZE(segment));
+  errno = saved_errno;
 }
 
 
@@ -74,16 +78,20 @@ void fast_free(void* segment)
  * This function is identical to `free`, except it is guaranteed to
  * override the memory segment with zeroes before freeing the allocation.
  * 
+ * `errno` is guaranteed not to be set.
+ * 
  * @param  segment  The memory segment to free.
  * 
  * @since  Always.
  */
 void secure_free(void* segment)
 {
+  int saved_errno = errno;
   if (segment == NULL)
     return;
   explicit_bzero(PURE_ALLOC(segment), PURE_SIZE(segment));
   fast_free(segment);
+  errno = saved_errno;
 }