diff --git a/changelog.md b/changelog.md
index d62e96bbed78b..378fd81d2d791 100644
--- a/changelog.md
+++ b/changelog.md
@@ -52,6 +52,8 @@
 
 - `writeStackTrace` is available in JS backend now.
 
+- Added `math.isNaN`.
+
 ## Language changes
 
 - `nimscript` now handles `except Exception as e`.
diff --git a/lib/pure/math.nim b/lib/pure/math.nim
index ccd766f46156a..949d06dbc235b 100644
--- a/lib/pure/math.nim
+++ b/lib/pure/math.nim
@@ -158,6 +158,14 @@ proc classify*(x: float): FloatClass =
     return fcSubnormal
   return fcNormal
 
+proc isNaN*(x: float): bool =
+  ## Returns whether `x` is a `NaN`, more efficiently than via `classify(x) == fcNan`.
+  ## Does not work with: `--passc:-ffast-math`.
+  runnableExamples:
+    doAssert NaN.isNaN
+    doAssert not Inf.isNaN
+  result = x != x
+
 proc almostEqual*[T: SomeFloat](x, y: T; unitsInLastPlace: Natural = 4): bool {.
       since: (1, 5), inline, noSideEffect.} =
   ## Checks if two float values are almost equal, using