diff --git a/src/macro_utils.jl b/src/macro_utils.jl
index 733b755..356194c 100644
--- a/src/macro_utils.jl
+++ b/src/macro_utils.jl
@@ -14,15 +14,27 @@ function _fused_pairs(expr::Expr)
     exprs_out = []
     for _expr in expr.args
         # TODO: should we retain LineNumberNode?
-        if _expr isa Symbol # ????????
-            return ""
-        end
+        # if _expr isa Symbol # ????????
+        #     error("???")
+        #     return ""
+        # end
         _expr isa LineNumberNode && continue
-        # @assert _expr isa Expr
+        if _expr.head == :for
+            error("Loops are not allowed inside fused blocks")
+        end
+        if _expr.head == :if
+            error("If-statements are not allowed inside fused blocks")
+        end
+        if _expr.head == :call
+            error("Function calls are not allowed inside fused blocks")
+        end
         if _expr.head == :macrocall && _expr.args[1] == Symbol("@__dot__")
             se = code_lowered_single_expression(_expr)
             margs = materialize_args(se)
             push!(exprs_out, :(Pair($(margs[1]), $(margs[2]))))
+        else
+            @show _expr
+            error("Uncaught edge case")
         end
     end
     if length(exprs_out) == 1
diff --git a/test/bm_fused_reads_vs_hard_coded.jl b/test/bm_fused_reads_vs_hard_coded.jl
index 173190e..5e72709 100644
--- a/test/bm_fused_reads_vs_hard_coded.jl
+++ b/test/bm_fused_reads_vs_hard_coded.jl
@@ -34,37 +34,16 @@ end
 function knl_multi_copyto_hard_coded!(X, Y, ::Val{nitems}) where {nitems}
     (; x1, x2, x3, x4, x5, x6, x7, x8, x9, x10) = X
     (; y1, y2, y3, y4, y5, y6, y7, y8, y9, y10) = Y
-    gidx = CUDA.threadIdx().x + (CUDA.blockIdx().x - 1) * CUDA.blockDim().x
-    if gidx < nitems
-        idx = gidx
-        y1[idx] = x1[idx] + x2[idx] + x3[idx] + x4[idx]
-        y2[idx] = x2[idx] + x3[idx] + x4[idx] + x5[idx]
-        y3[idx] = x3[idx] + x4[idx] + x5[idx] + x6[idx]
-        y4[idx] = x4[idx] + x5[idx] + x6[idx] + x7[idx]
-        y5[idx] = x5[idx] + x6[idx] + x7[idx] + x8[idx]
-        y6[idx] = x6[idx] + x7[idx] + x8[idx] + x9[idx]
-        y7[idx] = x7[idx] + x8[idx] + x9[idx] + x10[idx]
-    end
-    return nothing
-end
-
-function knl_multi_copyto_hard_coded!(X, Y, ::Val{nitems}) where {nitems}
-    (; x1, x2, x3, x4, x5, x6, x7, x8, x9, x10) = X
-    (; y1, y2, y3, y4, y5, y6, y7, y8, y9, y10) = Y
-    gidx = CUDA.threadIdx().x + (CUDA.blockIdx().x - 1) * CUDA.blockDim().x
-    if gidx < nitems
-        @inbounds begin
-            idx = gidx
-            y1[idx] = x1[idx] + x6[idx]
-            y2[idx] = x2[idx] + x7[idx]
-            y3[idx] = x3[idx] + x8[idx]
-            y4[idx] = x4[idx] + x9[idx]
-            y5[idx] = x5[idx] + x10[idx]
-            y6[idx] = y1[idx]
-            y7[idx] = y2[idx]
-            y8[idx] = y3[idx]
-            y9[idx] = y4[idx]
-            y10[idx] = y5[idx]
+    idx = CUDA.threadIdx().x + (CUDA.blockIdx().x - 1) * CUDA.blockDim().x
+    @inbounds begin
+        if idx ≤ nitems
+            y1[idx] = x1[idx] + x2[idx] + x3[idx] + x4[idx]
+            y2[idx] = x2[idx] + x3[idx] + x4[idx] + x5[idx]
+            y3[idx] = x3[idx] + x4[idx] + x5[idx] + x6[idx]
+            y4[idx] = x4[idx] + x5[idx] + x6[idx] + x7[idx]
+            y5[idx] = x5[idx] + x6[idx] + x7[idx] + x8[idx]
+            y6[idx] = x6[idx] + x7[idx] + x8[idx] + x9[idx]
+            y7[idx] = x7[idx] + x8[idx] + x9[idx] + x10[idx]
         end
     end
     return nothing
@@ -108,6 +87,19 @@ function perf_kernel_fused!(X, Y)
     end
 end
 
+test_kernel!(;
+    fused! = perf_kernel_fused!,
+    unfused! = perf_kernel_unfused!,
+    X,
+    Y,
+)
+test_kernel!(;
+    fused! = perf_kernel_hard_coded!,
+    unfused! = perf_kernel_unfused!,
+    X,
+    Y,
+)
+
 # Compile
 perf_kernel_unfused!(X, Y)
 perf_kernel_fused!(X, Y)
diff --git a/test/expr_errors_and_edge_cases.jl b/test/expr_errors_and_edge_cases.jl
new file mode 100644
index 0000000..8d8a543
--- /dev/null
+++ b/test/expr_errors_and_edge_cases.jl
@@ -0,0 +1,85 @@
+#=
+using Revise; include(joinpath("test", "expr_errors_and_edge_cases.jl"))
+=#
+using Test
+import MultiBroadcastFusion as MBF
+@testset "loops" begin
+    # loops are not allowed, because
+    # code transformation occurs at macro
+    # expansion time, and we can't generally
+    # know how many times the loop will be
+    # executed at this time.
+
+    # We could try to specialize on literal ranges, e.g.,
+    # `for i in 1:10`, but that is likely an uncommon
+    # edge case.
+
+    expr_in = quote
+        @. y1 = x1 + x2 + x3 + x4
+        for i in 1:10
+            @. y2 = x2 + x3 + x4 + x5
+        end
+        @. y1 = x1 + x2 + x3 + x4
+    end
+    @test_throws ErrorException("Loops are not allowed inside fused blocks") MBF.fused_pairs(
+        expr_in,
+    )
+end
+
+struct Foo end
+
+@testset "If-statements" begin
+    # If-statements are not allowed, because
+    # code transformation occurs at macro
+    # expansion time, and Bools, even types,
+    # are not known at this time.
+
+    # We could specialize on literals, e.g.,
+    # `if true`, but that is likely an uncommon
+    # edge case.
+    foo = Foo()
+    expr_in = quote
+        @. y1 = x1 + x2 + x3 + x4
+        if foo isa Foo
+            @. y2 = x2 + x3 + x4 + x5
+        end
+        @. y1 = x1 + x2 + x3 + x4
+    end
+    @test_throws ErrorException(
+        "If-statements are not allowed inside fused blocks",
+    ) MBF.fused_pairs(expr_in)
+end
+
+bar() = nothing
+@testset "Function calls" begin
+    # Function calls are not allowed, because
+    # this could lead to subtle bugs (order of compute).
+    expr_in = quote
+        @. y1 = x1 + x2 + x3 + x4
+        bar()
+        @. y1 = x1 + x2 + x3 + x4
+    end
+    @test_throws ErrorException(
+        "Function calls are not allowed inside fused blocks",
+    ) MBF.fused_pairs(expr_in)
+end
+
+@testset "Comments" begin
+    expr_in = quote
+        @. y1 = x1 + x2 + x3 + x4
+        # Foo bar baz
+        # if i in 1:N
+        @. y2 = x2 + x3 + x4 + x5
+    end
+
+    expr_out = :((
+        Pair(y1, Base.broadcasted(+, x1, x2, x3, x4)),
+        Pair(y2, Base.broadcasted(+, x2, x3, x4, x5)),
+    ))
+    @test MBF.fused_pairs(expr_in) == expr_out
+end
+
+@testset "Empty" begin
+    expr_in = quote end
+    @test MBF.fused_pairs(expr_in) == :(())
+end
diff --git a/test/runtests.jl b/test/runtests.jl
index 0e2cc9f..8de2eec 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -4,23 +4,13 @@ using Revise; include(joinpath("test", "runtests.jl"))
 using Test
 using SafeTestsets
 
-@safetestset "expr_code_lowered_single_expression" begin
-    @time include("expr_code_lowered_single_expression.jl")
-end
-@safetestset "expr_materialize_args" begin
-    @time include("expr_materialize_args.jl")
-end
-@safetestset "expr_fused_pairs" begin
-    @time include("expr_fused_pairs.jl")
-end
-# TODO: add assertion test for Pairs that test against loops/if-else blocks
+#! format: off
+@safetestset "expr_code_lowered_single_expression" begin; @time include("expr_code_lowered_single_expression.jl"); end
+@safetestset "expr_materialize_args" begin; @time include("expr_materialize_args.jl"); end
+@safetestset "expr_fused_pairs" begin; @time include("expr_fused_pairs.jl"); end
+@safetestset "expr_errors_and_edge_cases" begin; @time include("expr_errors_and_edge_cases.jl"); end
 
-@safetestset "fused_shared_reads" begin
-    @time include("bm_fused_shared_reads.jl")
-end
-@safetestset "fused_shared_reads_writes" begin
-    @time include("bm_fused_shared_reads_writes.jl")
-end
-@safetestset "bm_fused_reads_vs_hard_coded" begin
-    @time include("bm_fused_reads_vs_hard_coded.jl")
-end
+@safetestset "fused_shared_reads" begin; @time include("bm_fused_shared_reads.jl"); end
+@safetestset "fused_shared_reads_writes" begin; @time include("bm_fused_shared_reads_writes.jl"); end
+@safetestset "bm_fused_reads_vs_hard_coded" begin; @time include("bm_fused_reads_vs_hard_coded.jl"); end
+#! format: on