diff --git a/src/changes/changes.xml b/src/changes/changes.xml
index 2620bc7aa..13193e5d1 100644
--- a/src/changes/changes.xml
+++ b/src/changes/changes.xml
@@ -54,6 +54,10 @@ If the output is not quite correct, check for invisible trailing spaces!
     </release>
 
     <release version="4.0" date="XXXX-XX-XX" description="">
+      <action dev="erans" type="fix" issue="MATH-1231">
+        Lifted unnecessary restriction on constructor's argument of
+        "MicrosphereInterpolator" (package "o.a.c.m.analysis.interpolation").
+      </action>
       <action dev="luc" type="fix" issue="MATH-1232"> <!-- backported to 3.6 -->
         Fixed error message for unknown parameter name in ODE.
       </action>
diff --git a/src/main/java/org/apache/commons/math4/analysis/interpolation/MicrosphereInterpolatingFunction.java b/src/main/java/org/apache/commons/math4/analysis/interpolation/MicrosphereInterpolatingFunction.java
index 9e754a906..ff468a29c 100644
--- a/src/main/java/org/apache/commons/math4/analysis/interpolation/MicrosphereInterpolatingFunction.java
+++ b/src/main/java/org/apache/commons/math4/analysis/interpolation/MicrosphereInterpolatingFunction.java
@@ -144,7 +144,7 @@ public class MicrosphereInterpolatingFunction
      */
     public MicrosphereInterpolatingFunction(double[][] xval,
                                             double[] yval,
-                                            int brightnessExponent,
+                                            double brightnessExponent,
                                             int microsphereElements,
                                             UnitSphereRandomVectorGenerator rand)
         throws DimensionMismatchException,
diff --git a/src/main/java/org/apache/commons/math4/analysis/interpolation/MicrosphereInterpolator.java b/src/main/java/org/apache/commons/math4/analysis/interpolation/MicrosphereInterpolator.java
index 0cc54f151..9ff4e84ea 100644
--- a/src/main/java/org/apache/commons/math4/analysis/interpolation/MicrosphereInterpolator.java
+++ b/src/main/java/org/apache/commons/math4/analysis/interpolation/MicrosphereInterpolator.java
@@ -40,7 +40,7 @@ public class MicrosphereInterpolator
     /**
      * Default exponent used the weights calculation.
      */
-    public static final int DEFAULT_BRIGHTNESS_EXPONENT = 2;
+    public static final double DEFAULT_BRIGHTNESS_EXPONENT = 2d;
     /**
      * Number of surface elements of the microsphere.
      */
@@ -49,7 +49,7 @@ public class MicrosphereInterpolator
      * Exponent used in the power law that computes the weights of the
      * sample data.
      */
-    private final int brightnessExponent;
+    private final double brightnessExponent;
 
     /**
      * Create a microsphere interpolator with default settings.
@@ -70,7 +70,7 @@ public class MicrosphereInterpolator
      * @throws NotStrictlyPositiveException if {@code elements <= 0}.
      */
     public MicrosphereInterpolator(final int elements,
-                                   final int exponent)
+                                   final double exponent)
         throws NotPositiveException,
                NotStrictlyPositiveException {
         if (exponent < 0) {
diff --git a/src/test/java/org/apache/commons/math4/analysis/interpolation/MicrosphereInterpolatorTest.java b/src/test/java/org/apache/commons/math4/analysis/interpolation/MicrosphereInterpolatorTest.java
index eab4faa28..1fd798d05 100644
--- a/src/test/java/org/apache/commons/math4/analysis/interpolation/MicrosphereInterpolatorTest.java
+++ b/src/test/java/org/apache/commons/math4/analysis/interpolation/MicrosphereInterpolatorTest.java
@@ -96,7 +96,7 @@ public final class MicrosphereInterpolatorTest {
                 }
             };
 
-        MultivariateInterpolator interpolator = new MicrosphereInterpolator();
+        MultivariateInterpolator interpolator = new MicrosphereInterpolator(567, 0.89);
 
         // Interpolating points in [-10, 10][-10, 10] by steps of 2.
         final int n = 121;