diff --git a/src/back/glsl/mod.rs b/src/back/glsl/mod.rs
index de0d83febf..19302f790e 100644
--- a/src/back/glsl/mod.rs
+++ b/src/back/glsl/mod.rs
@@ -2580,6 +2580,18 @@ impl<'a, W: Write> Writer<'a, W> {
 
                         write!(self.out, ")")?;
                     }
+                    // TODO: handle undefined behavior of BinaryOperator::Modulo
+                    //
+                    // sint:
+                    // if right == 0 return 0
+                    // if left == min(type_of(left)) && right == -1 return 0
+                    // if sign(left) == -1 || sign(right) == -1 return result as defined by WGSL
+                    //
+                    // uint:
+                    // if right == 0 return 0
+                    //
+                    // float:
+                    // if right == 0 return ? see https://github.com/gpuweb/gpuweb/issues/2798
                     BinaryOperation::Modulo => {
                         write!(self.out, "(")?;
 
diff --git a/src/back/hlsl/writer.rs b/src/back/hlsl/writer.rs
index 3701d0002a..2c1837761d 100644
--- a/src/back/hlsl/writer.rs
+++ b/src/back/hlsl/writer.rs
@@ -1795,6 +1795,20 @@ impl<'a, W: fmt::Write> super::Writer<'a, W> {
                 self.write_expr(module, left, func_ctx)?;
                 write!(self.out, ")")?;
             }
+
+            // TODO: handle undefined behavior of BinaryOperator::Modulo
+            //
+            // sint:
+            // if right == 0 return 0
+            // if left == min(type_of(left)) && right == -1 return 0
+            // if sign(left) != sign(right) return result as defined by WGSL
+            //
+            // uint:
+            // if right == 0 return 0
+            //
+            // float:
+            // if right == 0 return ? see https://github.com/gpuweb/gpuweb/issues/2798
+
             // While HLSL supports float operands with the % operator it is only
             // defined in cases where both sides are either positive or negative.
             Expression::Binary {
diff --git a/src/back/msl/writer.rs b/src/back/msl/writer.rs
index 3448d0c002..2dd256afb8 100644
--- a/src/back/msl/writer.rs
+++ b/src/back/msl/writer.rs
@@ -1482,6 +1482,20 @@ impl<W: Write> Writer<W> {
                     .resolve_type(left)
                     .scalar_kind()
                     .ok_or(Error::UnsupportedBinaryOp(op))?;
+
+                // TODO: handle undefined behavior of BinaryOperator::Modulo
+                //
+                // sint:
+                // if right == 0 return 0
+                // if left == min(type_of(left)) && right == -1 return 0
+                // if sign(left) == -1 || sign(right) == -1 return result as defined by WGSL
+                //
+                // uint:
+                // if right == 0 return 0
+                //
+                // float:
+                // if right == 0 return ? see https://github.com/gpuweb/gpuweb/issues/2798
+
                 if op == crate::BinaryOperator::Modulo && kind == crate::ScalarKind::Float {
                     write!(self.out, "{}::fmod(", NAMESPACE)?;
                     self.put_expression(left, context, true)?;
diff --git a/src/back/spv/block.rs b/src/back/spv/block.rs
index d492ddf53c..d302811db3 100644
--- a/src/back/spv/block.rs
+++ b/src/back/spv/block.rs
@@ -529,8 +529,15 @@ impl<'w> BlockContext<'w> {
                         _ => unimplemented!(),
                     },
                     crate::BinaryOperator::Modulo => match left_ty_inner.scalar_kind() {
+                        // TODO: handle undefined behavior
+                        // if right == 0 return 0
+                        // if left == min(type_of(left)) && right == -1 return 0
                         Some(crate::ScalarKind::Sint) => spirv::Op::SRem,
+                        // TODO: handle undefined behavior
+                        // if right == 0 return 0
                         Some(crate::ScalarKind::Uint) => spirv::Op::UMod,
+                        // TODO: handle undefined behavior
+                        // if right == 0 return ? see https://github.com/gpuweb/gpuweb/issues/2798
                         Some(crate::ScalarKind::Float) => spirv::Op::FRem,
                         _ => unimplemented!(),
                     },