diff --git a/core/src/processing/core/PApplet.java b/core/src/processing/core/PApplet.java
index 847291e1d..17aef6038 100644
--- a/core/src/processing/core/PApplet.java
+++ b/core/src/processing/core/PApplet.java
@@ -4802,7 +4802,16 @@ public class PApplet implements PConstants {
   static public final float map(float value,
                                 float start1, float stop1,
                                 float start2, float stop2) {
-    return start2 + (stop2 - start2) * ((value - start1) / (stop1 - start1));
+    float outgoing =
+      start2 + (stop2 - start2) * ((value - start1) / (stop1 - start1));
+    if (!Float.isFinite(outgoing)) {
+      final String msg =
+        String.format("map(%s, %s, %s, %s, %s) called, " +
+                      "which returns NaN or infinity",
+                      nf(value), nf(start1), nf(stop1), nf(start2), nf(stop2));
+      PGraphics.showWarning(msg);
+    }
+    return outgoing;
   }
 
 
@@ -9196,6 +9205,24 @@ public class PApplet implements PConstants {
   // INT NUMBER FORMATTING
 
 
+  static public String nf(float num) {
+    int inum = (int) num;
+    if (num == inum) {
+      return str(inum);
+    }
+    return str(num);
+  }
+
+
+  static public String[] nf(float[] num) {
+    String[] outgoing = new String[num.length];
+    for (int i = 0; i < num.length; i++) {
+      outgoing[i] = nf(num[i]);
+    }
+    return outgoing;
+  }
+
+
   /**
    * Integer number formatter.
    */
diff --git a/core/todo.txt b/core/todo.txt
index b0e6a0759..edc739991 100644
--- a/core/todo.txt
+++ b/core/todo.txt
@@ -4,6 +4,8 @@
 opengl
 X IndexOutOfBoundsException with pixelDensity(2) and P2D
 X   https://github.com/processing/processing/issues/3568
+X Shaders output to bottom left corner rather than full window in 3.0b2
+X   https://github.com/processing/processing/issues/3572
 _ `focused` variable always false in P2D/P3D
 _   https://github.com/processing/processing/issues/3564
 _ Use PBOs for async texture copy