diff --git a/src/AllocCheck.jl b/src/AllocCheck.jl
index 5834dd5..96a77fa 100644
--- a/src/AllocCheck.jl
+++ b/src/AllocCheck.jl
@@ -162,6 +162,9 @@ function find_allocs!(mod::LLVM.Module, meta, entry_name::String; ignore_throw=t
                         bt = backtrace_(inst; compiled)
                         fname = replace(name(decl), r"^ijl_"=>"jl_")
                         push!(errors, AllocatingRuntimeCall(fname, bt))
+                    elseif class === :unresolved
+                        bt = backtrace_(inst; compiled)
+                        push!(errors, UnresolvedRuntimeCall(bt))
                     end
 
                     if decl isa LLVM.Function && length(blocks(decl)) > 0 && !in(decl, seen)
diff --git a/src/classify.jl b/src/classify.jl
index 72b59cf..eaa8078 100644
--- a/src/classify.jl
+++ b/src/classify.jl
@@ -13,7 +13,7 @@ perform allocation, but which might allocate to get its job done (e.g. jl_subtyp
 function classify_runtime_fn(name::AbstractString; ignore_throw::Bool)
     match_ = match(r"^(ijl_|jl_)(.*)$", name)
 
-    isnothing(match_) && return (:unknown, false)
+    isnothing(match_) && return (:none, false)
     name = match_[2]
 
     may_alloc = fn_may_allocate(name; ignore_throw)
@@ -28,8 +28,10 @@ function classify_runtime_fn(name::AbstractString; ignore_throw::Bool)
                     "f__call_in_world", "f__call_in_world_total", "f_intrinsic_call", "f_invoke",
                     "f_opaque_closure_call", "apply", "apply_generic", "gf_invoke",
                     "gf_invoke_by_method", "gf_invoke_lookup_worlds", "invoke", "invoke_api",
-                    "call", "call0", "call1", "call2", "call3", "unknown_fptr")
+                    "call", "call0", "call1", "call2", "call3")
         return (:dispatch, may_alloc)
+    elseif name == "unknown_fptr"
+        return (:unresolved, false)
     else
         return (:runtime, may_alloc)
     end
@@ -222,7 +224,7 @@ and replace it with a new locally-declared function that has the
 resolved name as its identifier.
 """
 function rename_call!(call::LLVM.CallInst, mod::LLVM.Module)
-    callee = called_operand(call)
+    callee = LLVM.called_operand(call)
     if isa(callee, LLVM.LoadInst)
 
         fn_got = unwrap_ptr_casts(operands(callee)[1])
@@ -252,7 +254,7 @@ function rename_call!(call::LLVM.CallInst, mod::LLVM.Module)
         # Call to a runtime-determined function pointer, usually an OpaqueClosure
         # or a ccall that we were not able to fully resolve.
         #
-        # We label this as a DynamicDispatch to an unknown function target.
+        # We label this as an UnresolvedRuntimeCall, and request that the user report our bug
         fname = "jl_unknown_fptr"
     end
 
diff --git a/src/types.jl b/src/types.jl
index 953a233..ac346a2 100644
--- a/src/types.jl
+++ b/src/types.jl
@@ -1,3 +1,20 @@
+struct UnresolvedRuntimeCall
+    backtrace::Vector{Base.StackTraces.StackFrame}
+end
+
+Base.hash(self::UnresolvedRuntimeCall, h::UInt) = nice_hash(self.backtrace, h)
+Base.:(==)(self::UnresolvedRuntimeCall, other::UnresolvedRuntimeCall) = nice_isequal(self.backtrace,other.backtrace)
+
+function Base.show(io::IO, call::UnresolvedRuntimeCall)
+    if length(call.backtrace) == 0
+        Base.printstyled(io, "Unresolved runtime call", color=:red, bold=true)
+    else
+        Base.printstyled(io, "Unresolved runtime call", color=:red, bold=true)
+        Base.println(io, " in ", call.backtrace[1].file, ":", call.backtrace[1].line)
+        show_backtrace_and_excerpt(io, call.backtrace)
+    end
+    Base.println(io, " (This is an AllocCheck.jl bug, please report it at https://github.com/JuliaLang/AllocCheck.jl/issues)")
+end
 
 struct AllocatingRuntimeCall
     name::String
diff --git a/test/runtests.jl b/test/runtests.jl
index d5c86c1..fb5af92 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,5 +1,5 @@
 using AllocCheck
-using AllocCheck: AllocatingRuntimeCall, DynamicDispatch, AllocationSite
+using AllocCheck: AllocatingRuntimeCall, DynamicDispatch, AllocationSite, UnresolvedRuntimeCall
 using Test
 
 mutable struct Foo{T}
@@ -75,7 +75,7 @@ end
               for alloc in allocs)
 
     allocs = check_allocs(call_opaque_closure, (Int, Int); ignore_throw = false)
-    @test length(allocs) > 0 && any(alloc isa DynamicDispatch for alloc in allocs)
+    @test length(allocs) > 0 && any(alloc isa UnresolvedRuntimeCall for alloc in allocs)
 end
 
 @testset "@check_allocs macro (syntax)" begin
@@ -205,11 +205,11 @@ end
         @test  any(x isa AllocationSite && x.type == Memory        # uses jl_genericmemory_copy_slice
                    for x in check_allocs(copy, (Vector{Int},)))
 
-        @test  all(x isa DynamicDispatch || (x isa AllocationSite && x.type == Memory{UInt8}) # uses jl_string_to_genericmemory
+        @test  all(x isa UnresolvedRuntimeCall || (x isa AllocationSite && x.type == Memory{UInt8}) # uses jl_string_to_genericmemory
                    for x in check_allocs(Base.array_new_memory, (Memory{UInt8}, Int)))
 
         # Marked broken because the `Expr(:foreigncall, QuoteNode(:jl_alloc_string), ...)` should be resolved
-        # by AllocCheck.jl, but is instead (conservatively) marked as a DynamicDisaptch.
+        # by AllocCheck.jl, but is instead (conservatively) marked as a UnresolvedRuntimeCall
         #
         # We get thrown off by the `jl_load_and_lookup` machinery here.
         @test_broken all(x isa AllocationSite && x.type == Memory{UInt8} # uses jl_string_to_genericmemory