diff --git a/hphp/hack/hhi/stdlib/builtins_math.hhi b/hphp/hack/hhi/stdlib/builtins_math.hhi
index d2fb00ada15682..ee821d7b8dc850 100644
--- a/hphp/hack/hhi/stdlib/builtins_math.hhi
+++ b/hphp/hack/hhi/stdlib/builtins_math.hhi
@@ -32,7 +32,7 @@ const float M_LNPI;
 const float M_EULER;
 
 <<__PHPStdLib>>
-function pi()[]: HH\FIXME\MISSING_RETURN_TYPE;
+function pi()[]: float;
 <<__PHPStdLib>>
 function min(
   HH\FIXME\MISSING_PARAM_TYPE $value,
@@ -48,9 +48,9 @@ function abs(
   HH\FIXME\MISSING_PARAM_TYPE $number,
 )[]: HH\FIXME\MISSING_RETURN_TYPE;
 <<__PHPStdLib>>
-function is_finite(float $val)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function is_finite(float $val)[]: bool;
 <<__PHPStdLib>>
-function is_infinite(float $val)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function is_infinite(float $val)[]: bool;
 <<__PHPStdLib>>
 function is_nan(float $val)[]: bool;
 <<__PHPStdLib>>
@@ -97,51 +97,51 @@ function base_convert(
 )[]: HH\FIXME\MISSING_RETURN_TYPE;
 <<__PHPStdLib>>
 function pow(
-  HH\FIXME\MISSING_PARAM_TYPE $base,
-  HH\FIXME\MISSING_PARAM_TYPE $exp,
-)[]: HH\FIXME\MISSING_RETURN_TYPE;
+  num $base,
+  num $exp,
+)[]: dynamic;
 <<__PHPStdLib>>
-function exp(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function exp(float $arg)[]: float;
 <<__PHPStdLib>>
-function expm1(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function expm1(float $arg)[]: float;
 <<__PHPStdLib>>
-function log10(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function log10(float $arg)[]: float;
 <<__PHPStdLib>>
-function log1p(float $number)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function log1p(float $number)[]: float;
 <<__PHPStdLib>>
-function log(float $arg, float $base = 0.0)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function log(float $arg, float $base = 0.0)[]: float;
 <<__PHPStdLib>>
-function cos(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function cos(float $arg)[]: float;
 <<__PHPStdLib>>
-function cosh(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function cosh(float $arg)[]: float;
 <<__PHPStdLib>>
-function sin(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function sin(float $arg)[]: float;
 <<__PHPStdLib>>
-function sinh(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function sinh(float $arg)[]: float;
 <<__PHPStdLib>>
-function tan(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function tan(float $arg)[]: float;
 <<__PHPStdLib>>
-function tanh(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function tanh(float $arg)[]: float;
 <<__PHPStdLib>>
-function acos(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function acos(float $arg)[]: float;
 <<__PHPStdLib>>
-function acosh(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function acosh(float $arg)[]: float;
 <<__PHPStdLib>>
-function asin(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function asin(float $arg)[]: float;
 <<__PHPStdLib>>
-function asinh(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function asinh(float $arg)[]: float;
 <<__PHPStdLib>>
-function atan(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function atan(float $arg)[]: float;
 <<__PHPStdLib>>
-function atanh(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function atanh(float $arg)[]: float;
 <<__PHPStdLib>>
-function atan2(float $y, float $x)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function atan2(float $y, float $x)[]: float;
 <<__PHPStdLib>>
-function hypot(float $x, float $y)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function hypot(float $x, float $y)[]: float;
 <<__PHPStdLib>>
-function fmod(float $x, float $y)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function fmod(float $x, float $y)[]: float;
 <<__PHPStdLib>>
-function sqrt(float $arg)[]: HH\FIXME\MISSING_RETURN_TYPE;
+function sqrt(float $arg)[]: float;
 <<__PHPStdLib>>
 function getrandmax()[]: HH\FIXME\MISSING_RETURN_TYPE;
 <<__PHPStdLib>>
diff --git a/hphp/hack/test/autocomplete/def_function.php.exp b/hphp/hack/test/autocomplete/def_function.php.exp
index d0b409659edffd..31dc757cd56ad8 100644
--- a/hphp/hack/test/autocomplete/def_function.php.exp
+++ b/hphp/hack/test/autocomplete/def_function.php.exp
@@ -243,7 +243,7 @@ flush
   (function(): ~HH\FIXME\MISSING_RETURN_TYPE)
 fmod
   INSERT fmod(${1:\$x}, ${2:\$y})
-  (function(float $x, float $y): ~HH\FIXME\MISSING_RETURN_TYPE)
+  (function(float $x, float $y): float)
 fnmatch
   INSERT fnmatch(${1:\$pattern}, ${2:\$filename})
   (function(string $pattern, string $filename, int $flags = _): ~HH\FIXME\MISSING_RETURN_TYPE)
diff --git a/hphp/hack/test/autocomplete/def_function_after_class.php.exp b/hphp/hack/test/autocomplete/def_function_after_class.php.exp
index d0b409659edffd..31dc757cd56ad8 100644
--- a/hphp/hack/test/autocomplete/def_function_after_class.php.exp
+++ b/hphp/hack/test/autocomplete/def_function_after_class.php.exp
@@ -243,7 +243,7 @@ flush
   (function(): ~HH\FIXME\MISSING_RETURN_TYPE)
 fmod
   INSERT fmod(${1:\$x}, ${2:\$y})
-  (function(float $x, float $y): ~HH\FIXME\MISSING_RETURN_TYPE)
+  (function(float $x, float $y): float)
 fnmatch
   INSERT fnmatch(${1:\$pattern}, ${2:\$filename})
   (function(string $pattern, string $filename, int $flags = _): ~HH\FIXME\MISSING_RETURN_TYPE)
diff --git a/hphp/hack/test/integration_ml/test_server_hover.ml b/hphp/hack/test/integration_ml/test_server_hover.ml
index 906935ef07def5..405974be18a295 100644
--- a/hphp/hack/test/integration_ml/test_server_hover.ml
+++ b/hphp/hack/test/integration_ml/test_server_hover.ml
@@ -53,20 +53,20 @@ abstract class ClassMembers {
 //         ^30:12
     await ClassMembers::genLotsOfModifiers();
 //        ^32:11        ^32:25
-    $this->calculateDistance(5, -6, 12, 1);
+    $this->calculateDistance(5.0, -6.0, 12.0, 1.0);
 //                         ^34:28
   }
 
   /** Another method doc block */
   public function calculateDistance(
-    int $originalPositionX,
-    int $finalPositionX,
-    int $originalPositionY,
-    int $finalPositionY,
-  ): int {
+    float $originalPositionX,
+    float $finalPositionX,
+    float $originalPositionY,
+    float $finalPositionY,
+  ): float {
     return sqrt(
-      pow($originalPositionX - $finalPositionX, 2) +
-        pow($originalPositionY - $finalPositionY, 2),
+      (float)pow($originalPositionX - $finalPositionX, 2) +
+        (float)pow($originalPositionY - $finalPositionY, 2),
     );
   }
 }
@@ -156,11 +156,11 @@ let class_members_cases =
           snippet =
             "// Defined in ClassMembers\n"
             ^ "public function calculateDistance(\n"
-            ^ "  int $originalPositionX,\n"
-            ^ "  int $finalPositionX,\n"
-            ^ "  int $originalPositionY,\n"
-            ^ "  int $finalPositionY\n"
-            ^ "): int";
+            ^ "  float $originalPositionX,\n"
+            ^ "  float $finalPositionX,\n"
+            ^ "  float $originalPositionY,\n"
+            ^ "  float $finalPositionY\n"
+            ^ "): float";
           addendum = ["Another method doc block"];
           pos = pos_at (34, 12) (34, 28);
         };
diff --git a/hphp/runtime/ext/std/ext_std_math.php b/hphp/runtime/ext/std/ext_std_math.php
index 88100c6c7058e0..198ccba8c55ef8 100644
--- a/hphp/runtime/ext/std/ext_std_math.php
+++ b/hphp/runtime/ext/std/ext_std_math.php
@@ -289,8 +289,8 @@ function base_convert(mixed $number, int $frombase, int $tobase)[]: mixed;
  * Returns base raised to the power of exp. Warning  In PHP 4.0.6 and earlier
  *   pow() always returned a float, and did not issue warnings.
  *
- * @param mixed $base - The base to use
- * @param mixed $exp - The exponent
+ * @param num $base - The base to use
+ * @param num $exp - The exponent
  *
  * @return mixed - base raised to the power of exp. If the result can be
  *   represented as integer it will be returned as type integer, else it will be
@@ -299,7 +299,7 @@ function base_convert(mixed $number, int $frombase, int $tobase)[]: mixed;
  *
  */
 <<__IsFoldable, __Native>>
-function pow(mixed $base, mixed $exp)[]: mixed;
+function pow(num $base, num $exp)[]: mixed;
 
 /**
  * Returns e raised to the power of arg.  'e' is the base of the natural