diff --git a/extensions/NV/NV_compute_shader_derivatives.txt b/extensions/NV/NV_compute_shader_derivatives.txt
index 4bc891b..bdd9f6c 100644
--- a/extensions/NV/NV_compute_shader_derivatives.txt
+++ b/extensions/NV/NV_compute_shader_derivatives.txt
@@ -22,8 +22,8 @@
 
 Version
 
-    Last Modified:      November 9, 2018
-    Revision:           2
+    Last Modified:      September 4, 2019
+    Revision:           3
 
 Number
 
@@ -37,6 +37,8 @@
 
     OpenGL 4.5 or OpenGL ES 3.2 is required.
 
+    This extension interacts with ARB_compute_variable_group_size.
+
     This extension requires support for the OpenGL Shading Language (GLSL)
     extension "NV_compute_shader_derivatives", which can be found at the
     Khronos Group Github site here:
@@ -88,12 +90,62 @@
 
     None
 
+Dependencies on ARB_compute_variable_group_size
+
+    If ARB_compute_variable_group_size is supported, the GLSL compiler/linker is
+    unable to enforce the following restrictions:
+
+    * Compute shaders using the "derivative_group_quadsNV" mode must have a
+      local workgroup size whose width and height are both multiples of two.
+
+    * Compute shaders using the "derivative_group_linearNV" mode must have a
+      local workgroup size whose total number of invocations is a multiple of four.
+
+    Instead, we need to enforce this restriction at run time.
+
+    Add the following to the list of errors under the heading of "insert at the
+    end of the first error block, shared between DispatchCompute and
+    DispatchComputeGroupSizeARB, p. 586" in ARB_compute_variable_group_size:
+
+    * An INVALID_VALUE error is generated by DispatchComputeGroupSizeARB if the
+      active program for the compute shader stage has a compute shader using the
+      "derivative_group_quadsNV" layout qualifier and <group_size_x> or
+      <group_size_y> is not a multiple of two.
+
+    * An INVALID_VALUE error is generated by DispatchComputeGroupSizeARB if the
+      active program for the compute shader stage has a compute shader using the
+      "derivative_group_linearNV" layout qualifier and the product of
+      <group_size_x>, <group_size_y>, and <group_size_z> is not a multiple of
+      four.
+
+    Note that as of September 2019, this issue does not apply to SPIR-V compute
+    shaders because SPIR-V does not provide a mechanism to specify variable
+    local group sizes.  If this changes in the future, the INVALID_VALUE error
+    above would apply both to GLSL and SPIR-V compute shaders.
+
+
 Issues
 
-    None, but please refer to issues in the GLSL extension specification.
+    (1) How does this extension interact with ARB_compute_variable_group_size?
+
+      RESOLVED:  For compute shaders with fixed group size, the GLSL
+      specification calls for a compile- or link-time error if the local group
+      size is inconsistent with the derivative mode specified using the
+      "derivative_group_quadsNV" or "derivative_group_linearNV" layout
+      qualifiers.  However, this sort of error can not be generated if
+      "local_size_variable" is also specified because the local group size is
+      not known until DispatchComputeGroupSizeARB is called.  To deal with this,
+      we specify an INVALID_VALUE error if DispatchComputeGroupSizeARB is called
+      with a bad local group size.
 
 Revision History
 
+    Revision 3 (pbrown), 2019/09/04
+    - Add an interaction with ARB_compute_variable_group_size, specifying
+      that INVALID_VALUE is generated by DispatchComputeGroupSizeARB if the
+      derivative mode is inconsistent with the local group size specified in the
+      dispatch command.
+
     Revision 2 (mchock)
     - Added OpenGL ES support.