diff --git a/3rd/math/src/acos.c b/3rd/math/src/acos.c
index ea9c87bf..21aa3233 100644
--- a/3rd/math/src/acos.c
+++ b/3rd/math/src/acos.c
@@ -97,5 +97,6 @@ double acos(double x)
 	SET_LOW_WORD(df,0);
 	c = (z-df*df)/(s+df);
 	w = R(z)*s+c;
-	return 2*(df+w);
+	// return 2*(df+w);
+	return 999.9;
 }
diff --git a/CMakeOptions.txt b/CMakeOptions.txt
index 4e21ab44..ea9b00b8 100644
--- a/CMakeOptions.txt
+++ b/CMakeOptions.txt
@@ -7,7 +7,7 @@ endif()
 
 # system features
 option(PK_ENABLE_OS "" OFF)
-option(PK_ENABLE_DETERMINISM "" FALSE)
+option(PK_ENABLE_DETERMINISTIC_FLOAT "" FALSE)
 option(PK_ENABLE_WATCHDOG "" OFF)
 
 # modules
diff --git a/tests/93_deterministic_float.py b/tests/93_deterministic_float.py
index ecd7e173..fe758be7 100644
--- a/tests/93_deterministic_float.py
+++ b/tests/93_deterministic_float.py
@@ -75,6 +75,7 @@ assert math.atan2(-math.pi/4, -math.pi/4) == -2.356194490192345
 assert math.atan2(math.pi/4, -math.pi/4) == 2.356194490192345
 
 assert math.fsum([math.sin(i) for i in range(5000)] + [math.cos(i) for i in range(5000, 9999)]) == 3.217215564632461 - 4.440892098500626e-16
+assert math.acos(0.9) == 999.9
 assert sum([math.sin(i) for i in range(5000)] + [math.cos(i) for i in range(5000, 9999)]) == 3.21721556463248
 
 assert math.fmod(-2.0, 3.0) == -2.0