diff --git a/libcore/luni/src/main/java/java/lang/Math.java b/libcore/luni/src/main/java/java/lang/Math.java
index 26019ec..d286d20 100644
--- a/libcore/luni/src/main/java/java/lang/Math.java
+++ b/libcore/luni/src/main/java/java/lang/Math.java
@@ -1091,47 +1091,25 @@
     private native static double nextafter(double x, double y);
 
     private native static float nextafterf(float x, float y);
-    
-    /**
-     * Answers a result of the magnitude of the first given double value and the
-     * sign of the second given double value.
-     * 
-     * @param magnitude
-     *            the double value whose magnitude should be used
-     * @param sign
-     *            the double value whose sign should be used
-     * @return a result of the magnitude of the first given double value and the
-     *         sign of the second given double value .
-     * 
-     * @since 1.6
-     * @hide
-     */
-    public static double copySign(double magnitude, double sign) {
-        long mbits = Double.doubleToRawLongBits(magnitude);
-        long sbits = Double.doubleToRawLongBits(sign);
-        return Double.longBitsToDouble((mbits & ~DOUBLE_SIGN_MASK) | (sbits & DOUBLE_SIGN_MASK));
-    }
 
     /**
-     * Answers a result of the magnitude of the first given float value and the
-     * sign of the second given float value .
-     * 
-     * @param magnitude
-     *            the float value whose magnitude should be used
-     * @param sign
-     *            the float value whose sign should be used
-     * @return a result with the magnitude of the first given float value and
-     *         the sign of the second given float value .
-     * 
+     * Returns a double with the given magnitude and the sign of {@code sign}.
+     * If {@code sign} is NaN, the sign of the result is arbitrary.
+     * If you need a determinate sign in such cases, use {@code StrictMath.copySign}.
      * @since 1.6
      * @hide
      */
-    public static float copySign(float magnitude, float sign) {
-        int mbits = Float.floatToRawIntBits(magnitude);
-        int sbits = Float.floatToRawIntBits(sign);
-        return Float.intBitsToFloat((mbits & ~FLOAT_SIGN_MASK) | (sbits & FLOAT_SIGN_MASK));
-    }
-    
+    public static native double copySign(double magnitude, double sign);
+
+    /**
+     * Returns a float with the given magnitude and the sign of {@code sign}.
+     * If {@code sign} is NaN, the sign of the result is arbitrary.
+     * If you need a determinate sign in such cases, use {@code StrictMath.copySign}.
+     * @since 1.6
+     * @hide
+     */
+    public static native float copySign(float magnitude, float sign);
+
     /**
      * Answers the exponent of a float.
      * 
diff --git a/libcore/luni/src/main/java/java/lang/StrictMath.java b/libcore/luni/src/main/java/java/lang/StrictMath.java
index 5d3ec8f..cd3c9b5 100644
--- a/libcore/luni/src/main/java/java/lang/StrictMath.java
+++ b/libcore/luni/src/main/java/java/lang/StrictMath.java
@@ -1037,41 +1037,21 @@
     private native static float nextafterf(float x, float y); 
     
     /**
-     * Answers a result of the magnitude of the first given double value and the
-     * sign of the second given double value.
-     * 
-     * @param magnitude
-     *            the double value whose magnitude should be used
-     * @param sign
-     *            the double value whose sign should be used
-     * @return a result of the magnitude of the first given double value and the
-     *         sign of the second given double value.
-     *         
+     * Returns a double with the given magnitude and the sign of {@code sign}.
+     * If {@code sign} is NaN, the sign of the result is positive.
      * @since 1.6
      * @hide
      */
-    public static double copySign(double magnitude, double sign) {
-        return Math.copySign(magnitude, sign);
-    }
+    public static native double copySign(double magnitude, double sign);
 
     /**
-     * Answers a result of the magnitude of the first given float value and the
-     * sign of the second given float value.
-     * 
-     * @param magnitude
-     *            the float value whose magnitude should be used
-     * @param sign
-     *            the float value whose sign should be used
-     * @return a result with the magnitude of the first given float value and
-     *         the sign of the second given float value.
-     *         
+     * Returns a float with the given magnitude and the sign of {@code sign}.
+     * If {@code sign} is NaN, the sign of the result is positive.
      * @since 1.6
      * @hide
      */
-    public static float copySign(float magnitude, float sign) {
-        return Math.copySign(magnitude, sign);
-    }
-    
+    public static native float copySign(float magnitude, float sign);
+
     /**
      * Answers the exponent of a float.
      * 
diff --git a/libcore/luni/src/main/native/java_lang_Math.c b/libcore/luni/src/main/native/java_lang_Math.c
index a3a69dd..35754cd 100644
--- a/libcore/luni/src/main/native/java_lang_Math.c
+++ b/libcore/luni/src/main/native/java_lang_Math.c
@@ -159,42 +159,46 @@
     return nextafterf(a, b);
 }
 
+static jdouble copySign(JNIEnv* env, jclass clazz, jdouble a, jdouble b) {
+    return copysign(a, b);
+}
+
+static jfloat copySign_f(JNIEnv* env, jclass clazz, jfloat a, jfloat b) {
+    return copysignf(a, b);
+}
+
 /*
  * JNI registration.
  */
 static JNINativeMethod gMethods[] = {
     /* name, signature, funcPtr */
-    { "sin",    "(D)D", jsin },
-    { "cos",    "(D)D", jcos },
-    { "tan",    "(D)D", jtan },
-
-    { "asin",   "(D)D", jasin },
-    { "acos",   "(D)D", jacos },
-    { "atan",   "(D)D", jatan },
-
-    { "exp",    "(D)D", jexp },
-    { "log",    "(D)D", jlog },
-    { "sqrt",   "(D)D", jsqrt },
-
     { "IEEEremainder", "(DD)D", jieee_remainder },
-
-    { "floor",  "(D)D", jfloor },
-    { "ceil",   "(D)D", jceil },
-    { "rint",   "(D)D", jrint },
-
+    { "acos",   "(D)D", jacos },
+    { "asin",   "(D)D", jasin },
+    { "atan",   "(D)D", jatan },
     { "atan2",  "(DD)D", jatan2 },
-    { "pow",    "(DD)D", jpow },
-
-    { "sinh",   "(D)D", jsinh },
-    { "cosh",   "(D)D", jcosh },
-    { "tanh",   "(D)D", jtanh },
-    { "log10",  "(D)D", jlog10 },
     { "cbrt",   "(D)D", jcbrt },
+    { "ceil",   "(D)D", jceil },
+    { "copySign",  "(DD)D", copySign },
+    { "copySign",  "(FF)F", copySign_f },
+    { "cos",    "(D)D", jcos },
+    { "cosh",   "(D)D", jcosh },
+    { "exp",    "(D)D", jexp },
     { "expm1",  "(D)D", jexpm1 },
+    { "floor",  "(D)D", jfloor },
     { "hypot",  "(DD)D", jhypot },
+    { "log",    "(D)D", jlog },
+    { "log10",  "(D)D", jlog10 },
     { "log1p",  "(D)D", jlog1p },
     { "nextafter",  "(DD)D", jnextafter },
     { "nextafterf",  "(FF)F", jnextafterf },
+    { "pow",    "(DD)D", jpow },
+    { "rint",   "(D)D", jrint },
+    { "sin",    "(D)D", jsin },
+    { "sinh",   "(D)D", jsinh },
+    { "sqrt",   "(D)D", jsqrt },
+    { "tan",    "(D)D", jtan },
+    { "tanh",   "(D)D", jtanh },
 };
 
 int register_java_lang_Math(JNIEnv* env)
diff --git a/libcore/luni/src/main/native/java_lang_StrictMath.c b/libcore/luni/src/main/native/java_lang_StrictMath.c
index 7d335f7..3839c21 100644
--- a/libcore/luni/src/main/native/java_lang_StrictMath.c
+++ b/libcore/luni/src/main/native/java_lang_StrictMath.c
@@ -8,7 +8,7 @@
 
 #include <stdlib.h>
 /* This static way is the "best" way to integrate fdlibm without a conflict
- * into the android envoirement 
+ * into the android environment.
  */
 
 /* #include "fltconst.h" */
@@ -20,6 +20,8 @@
 #include "../../external/fdlibm/fdlibm.h"
 _LIB_VERSION_TYPE _LIB_VERSION = _IEEE_;
 
+#include <math.h>
+
 /* native public static double sin(double a); */
 static jdouble jsin(JNIEnv* env, jclass clazz, jdouble a)
 {
@@ -184,42 +186,46 @@
     return arg1;
 }
 
+static jdouble copySign(JNIEnv* env, jclass clazz, jdouble a, jdouble b) {
+    return copysign(a, isnan(b) ? 1.0 : b);
+}
+
+static jfloat copySign_f(JNIEnv* env, jclass clazz, jfloat a, jfloat b) {
+    return copysignf(a, isnan(b) ? 1.0f : b);
+}
+
 /*
  * JNI registration.
  */
 static JNINativeMethod gMethods[] = {
     /* name, signature, funcPtr */
-    { "sin",    "(D)D", jsin },
-    { "cos",    "(D)D", jcos },
-    { "tan",    "(D)D", jtan },
-
-    { "asin",   "(D)D", jasin },
-    { "acos",   "(D)D", jacos },
-    { "atan",   "(D)D", jatan },
-
-    { "exp",    "(D)D", jexp },
-    { "log",    "(D)D", jlog },
-    { "sqrt",   "(D)D", jsqrt2 },
-
     { "IEEEremainder", "(DD)D", jieee_remainder },
-
-    { "floor",  "(D)D", jfloor },
-    { "ceil",   "(D)D", jceil },
-    { "rint",   "(D)D", jrint },
-
+    { "acos",   "(D)D", jacos },
+    { "asin",   "(D)D", jasin },
+    { "atan",   "(D)D", jatan },
     { "atan2",  "(DD)D", jatan2 },
-    { "pow",    "(DD)D", jpow },
-
-    { "sinh",   "(D)D", jsinh },
-    { "cosh",   "(D)D", jcosh },
-    { "tanh",   "(D)D", jtanh },
-    { "log10",  "(D)D", jlog10 },
     { "cbrt",   "(D)D", jcbrt },
+    { "ceil",   "(D)D", jceil },
+    { "copySign",  "(DD)D", copySign },
+    { "copySign",  "(FF)F", copySign_f },
+    { "cos",    "(D)D", jcos },
+    { "cosh",   "(D)D", jcosh },
+    { "exp",    "(D)D", jexp },
     { "expm1",  "(D)D", jexpm1 },
+    { "floor",  "(D)D", jfloor },
     { "hypot",  "(DD)D", jhypot },
+    { "log",    "(D)D", jlog },
+    { "log10",  "(D)D", jlog10 },
     { "log1p",  "(D)D", jlog1p },
     { "nextafter",  "(DD)D", jnextafter },
     { "nextafterf",  "(FF)F", jnextafterf },
+    { "pow",    "(DD)D", jpow },
+    { "rint",   "(D)D", jrint },
+    { "sin",    "(D)D", jsin },
+    { "sinh",   "(D)D", jsinh },
+    { "sqrt",   "(D)D", jsqrt2 },
+    { "tan",    "(D)D", jtan },
+    { "tanh",   "(D)D", jtanh },
 };
 
 int register_java_lang_StrictMath(JNIEnv* env)