3 files changed, 36 insertions, 3 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1c9e15e..2fd09d1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -27,6 +27,10 @@ The scope of what is covered by the version number excludes:
 
 ## Version history
 
+### version 0.6.0, unreleased
+
+- Fix: when sleep returns an error, pass that on in `readkey`.
+
 ### version 0.5.1, released 12-Mar-2025
 
 - Fix: on older unixes with glibc < 2.25, fall back to `/dev/urandom`
diff --git a/spec/04-term_spec.lua b/spec/04-term_spec.lua
index 907f903..b3de461 100644
--- a/spec/04-term_spec.lua
+++ b/spec/04-term_spec.lua
@@ -855,6 +855,32 @@ describe("Terminal:", function()
         assert.is.near(1, timing, 0.5)       -- this also works for MacOS in CI
       end)
 
+
+      it("calls flseep to execute the sleep", function()
+        setbuffer("")
+
+        local sleep_called = false
+        local mysleep = function()
+          sleep_called = true
+        end
+
+        system.readkey(0.01, mysleep)
+        assert.is_true(sleep_called)
+      end)
+
+
+      it("returns errors by fsleep", function()
+        setbuffer("")
+
+        local mysleep = function()
+          return nil, "boom!"
+        end
+
+        local ok, err = system.readkey(1, mysleep)
+        assert.is.falsy(ok)
+        assert.equals("boom!", err)
+      end)
+
     end)
 
 
diff --git a/system/init.lua b/system/init.lua
index a81978e..28fe65c 100644
--- a/system/init.lua
+++ b/system/init.lua
@@ -236,10 +236,10 @@ do
   -- Using `system.readansi` is preferred over this function. Since this function can leave stray/invalid
   -- byte-sequences in the input buffer, while `system.readansi` reads full ANSI and UTF8 sequences.
   -- @tparam number timeout the timeout in seconds.
-  -- @tparam[opt=system.sleep] function fsleep the function to call for sleeping.
+  -- @tparam[opt=system.sleep] function fsleep the function to call for sleeping; `ok, err = fsleep(secs)`
   -- @treturn[1] byte the byte value that was read.
   -- @treturn[2] nil if no key was read
-  -- @treturn[2] string error message; `"timeout"` if the timeout was reached.
+  -- @treturn[2] string error message when the timeout was reached (`"timeout"`), or if `sleep` failed.
   function system.readkey(timeout, fsleep)
     if type(timeout) ~= "number" then
       error("arg #1 to readkey, expected timeout in seconds, got " .. type(timeout), 2)
@@ -248,7 +248,10 @@ do
     local interval = 0.0125
     local key = system._readkey()
     while key == nil and timeout > 0 do
-      (fsleep or system.sleep)(math.min(interval, timeout))
+      local ok, err = (fsleep or system.sleep)(math.min(interval, timeout))
+      if not ok then
+        return nil, err
+      end
       timeout = timeout - interval
       interval = math.min(0.2, interval * 2)
       key = system._readkey()