diff --git a/cranelift/codegen/src/ir/libcall.rs b/cranelift/codegen/src/ir/libcall.rs
index 6734258ed7..e6b2d539d0 100644
--- a/cranelift/codegen/src/ir/libcall.rs
+++ b/cranelift/codegen/src/ir/libcall.rs
@@ -1,7 +1,7 @@
 //! Naming well-known routines in the runtime library.
 
 use crate::{
-    ir::{types, AbiParam, ExternalName, FuncRef, Function, Signature},
+    ir::{types, AbiParam, ExternalName, FuncRef, Function, Signature, Type},
     isa::CallConv,
 };
 use core::fmt;
@@ -119,7 +119,7 @@ impl LibCall {
     }
 
     /// Get a [Signature] for the function targeted by this [LibCall].
-    pub fn signature(&self, call_conv: CallConv) -> Signature {
+    pub fn signature(&self, call_conv: CallConv, pointer_type: Type) -> Signature {
         use types::*;
         let mut sig = Signature::new(call_conv);
 
@@ -140,13 +140,32 @@ impl LibCall {
                 sig.params.push(AbiParam::new(ty));
                 sig.returns.push(AbiParam::new(ty));
             }
-            LibCall::Probestack
-            | LibCall::Memcpy
-            | LibCall::Memset
-            | LibCall::Memmove
-            | LibCall::Memcmp
-            | LibCall::ElfTlsGetAddr
-            | LibCall::ElfTlsGetOffset => unimplemented!(),
+            LibCall::Memcpy | LibCall::Memmove => {
+                // void* memcpy(void *dest, const void *src, size_t count);
+                // void* memmove(void* dest, const void* src, size_t count);
+                sig.params.push(AbiParam::new(pointer_type));
+                sig.params.push(AbiParam::new(pointer_type));
+                sig.params.push(AbiParam::new(pointer_type));
+                sig.returns.push(AbiParam::new(pointer_type));
+            }
+            LibCall::Memset => {
+                // void *memset(void *dest, int ch, size_t count);
+                sig.params.push(AbiParam::new(pointer_type));
+                sig.params.push(AbiParam::new(I32));
+                sig.params.push(AbiParam::new(pointer_type));
+                sig.returns.push(AbiParam::new(pointer_type));
+            }
+            LibCall::Memcmp => {
+                // void* memcpy(void *dest, const void *src, size_t count);
+                sig.params.push(AbiParam::new(pointer_type));
+                sig.params.push(AbiParam::new(pointer_type));
+                sig.params.push(AbiParam::new(pointer_type));
+                sig.returns.push(AbiParam::new(I32))
+            }
+
+            LibCall::Probestack | LibCall::ElfTlsGetAddr | LibCall::ElfTlsGetOffset => {
+                unimplemented!()
+            }
         }
 
         sig
diff --git a/cranelift/codegen/src/isa/x64/lower.rs b/cranelift/codegen/src/isa/x64/lower.rs
index bd3b6e8dcd..d40eaecdc4 100644
--- a/cranelift/codegen/src/isa/x64/lower.rs
+++ b/cranelift/codegen/src/isa/x64/lower.rs
@@ -150,7 +150,7 @@ fn emit_vm_call(
 
     // TODO avoid recreating signatures for every single Libcall function.
     let call_conv = CallConv::for_libcall(flags, CallConv::triple_default(triple));
-    let sig = libcall.signature(call_conv);
+    let sig = libcall.signature(call_conv, types::I64);
     let caller_conv = ctx.abi().call_conv(ctx.sigs());
 
     if !ctx.sigs().have_abi_sig_for_signature(&sig) {
diff --git a/cranelift/codegen/src/isa/x64/lower/isle.rs b/cranelift/codegen/src/isa/x64/lower/isle.rs
index 1ca927ec31..bf328b5268 100644
--- a/cranelift/codegen/src/isa/x64/lower/isle.rs
+++ b/cranelift/codegen/src/isa/x64/lower/isle.rs
@@ -629,7 +629,7 @@ impl Context for IsleContext<'_, '_, MInst, X64Backend> {
 
     fn libcall_1(&mut self, libcall: &LibCall, a: Reg) -> Reg {
         let call_conv = self.lower_ctx.abi().call_conv(self.lower_ctx.sigs());
-        let ret_ty = libcall.signature(call_conv).returns[0].value_type;
+        let ret_ty = libcall.signature(call_conv, I64).returns[0].value_type;
         let output_reg = self.lower_ctx.alloc_tmp(ret_ty).only_reg().unwrap();
 
         emit_vm_call(
@@ -647,7 +647,7 @@ impl Context for IsleContext<'_, '_, MInst, X64Backend> {
 
     fn libcall_3(&mut self, libcall: &LibCall, a: Reg, b: Reg, c: Reg) -> Reg {
         let call_conv = self.lower_ctx.abi().call_conv(self.lower_ctx.sigs());
-        let ret_ty = libcall.signature(call_conv).returns[0].value_type;
+        let ret_ty = libcall.signature(call_conv, I64).returns[0].value_type;
         let output_reg = self.lower_ctx.alloc_tmp(ret_ty).only_reg().unwrap();
 
         emit_vm_call(
diff --git a/cranelift/frontend/src/frontend.rs b/cranelift/frontend/src/frontend.rs
index ecef10ba76..631f6ba8cb 100644
--- a/cranelift/frontend/src/frontend.rs
+++ b/cranelift/frontend/src/frontend.rs
@@ -753,6 +753,7 @@ impl<'a> FunctionBuilder<'a> {
             s.params.push(AbiParam::new(pointer_type));
             s.params.push(AbiParam::new(pointer_type));
             s.params.push(AbiParam::new(pointer_type));
+            s.returns.push(AbiParam::new(pointer_type));
             self.import_signature(s)
         };
 
@@ -853,6 +854,7 @@ impl<'a> FunctionBuilder<'a> {
             s.params.push(AbiParam::new(pointer_type));
             s.params.push(AbiParam::new(types::I32));
             s.params.push(AbiParam::new(pointer_type));
+            s.returns.push(AbiParam::new(pointer_type));
             self.import_signature(s)
         };
 
@@ -949,6 +951,7 @@ impl<'a> FunctionBuilder<'a> {
             s.params.push(AbiParam::new(pointer_type));
             s.params.push(AbiParam::new(pointer_type));
             s.params.push(AbiParam::new(pointer_type));
+            s.returns.push(AbiParam::new(pointer_type));
             self.import_signature(s)
         };
 
@@ -1283,15 +1286,15 @@ mod tests {
         check(
             &func,
             "function %sample() -> i32 system_v {
-    sig0 = (i64, i64, i64) system_v
+    sig0 = (i64, i64, i64) -> i64 system_v
     fn0 = %Memcpy sig0
 
 block0:
+    v4 = iconst.i64 0
+    v1 -> v4
     v3 = iconst.i64 0
-    v1 -> v3
-    v2 = iconst.i64 0
-    v0 -> v2
-    call fn0(v1, v0, v1)  ; v1 = 0, v0 = 0, v1 = 0
+    v0 -> v3
+    v2 = call fn0(v1, v0, v1)  ; v1 = 0, v0 = 0, v1 = 0
     return v1  ; v1 = 0
 }
 ",
@@ -1393,16 +1396,16 @@ block0:
         check(
             &func,
             "function %sample() -> i32 system_v {
-    sig0 = (i64, i64, i64) system_v
+    sig0 = (i64, i64, i64) -> i64 system_v
     fn0 = %Memcpy sig0
 
 block0:
+    v5 = iconst.i64 0
+    v1 -> v5
     v4 = iconst.i64 0
-    v1 -> v4
-    v3 = iconst.i64 0
-    v0 -> v3
+    v0 -> v4
     v2 = iconst.i64 8192
-    call fn0(v1, v0, v2)  ; v1 = 0, v0 = 0, v2 = 8192
+    v3 = call fn0(v1, v0, v2)  ; v1 = 0, v0 = 0, v2 = 8192
     return v1  ; v1 = 0
 }
 ",
@@ -1478,16 +1481,16 @@ block0:
         check(
             &func,
             "function %sample() -> i32 system_v {
-    sig0 = (i64, i32, i64) system_v
+    sig0 = (i64, i32, i64) -> i64 system_v
     fn0 = %Memset sig0
 
 block0:
-    v4 = iconst.i64 0
-    v0 -> v4
+    v5 = iconst.i64 0
+    v0 -> v5
     v1 = iconst.i8 1
     v2 = iconst.i64 8192
     v3 = uextend.i32 v1  ; v1 = 1
-    call fn0(v0, v3, v2)  ; v0 = 0, v2 = 8192
+    v4 = call fn0(v0, v3, v2)  ; v0 = 0, v2 = 8192
     return v0  ; v0 = 0
 }
 ",
diff --git a/cranelift/fuzzgen/src/function_generator.rs b/cranelift/fuzzgen/src/function_generator.rs
index 52f89db231..a6e28b73b8 100644
--- a/cranelift/fuzzgen/src/function_generator.rs
+++ b/cranelift/fuzzgen/src/function_generator.rs
@@ -1863,7 +1863,11 @@ where
             .libcalls
             .iter()
             .map(|libcall| {
-                let signature = libcall.signature(lib_callconv);
+                let pointer_type = Type::int_with_byte_size(
+                    self.target_triple.pointer_width().unwrap().bytes().into(),
+                )
+                .unwrap();
+                let signature = libcall.signature(lib_callconv, pointer_type);
                 let name = ExternalName::LibCall(*libcall);
                 (name, signature)
             })
diff --git a/cranelift/interpreter/src/state.rs b/cranelift/interpreter/src/state.rs
index 6e01d4b943..5c5d7a685b 100644
--- a/cranelift/interpreter/src/state.rs
+++ b/cranelift/interpreter/src/state.rs
@@ -5,8 +5,8 @@ use crate::frame::Frame;
 use crate::interpreter::LibCallHandler;
 use cranelift_codegen::data_value::DataValue;
 use cranelift_codegen::ir::{
-    ExternalName, FuncRef, Function, GlobalValue, LibCall, MemFlags, Signature, StackSlot, Type,
-    Value,
+    types, ExternalName, FuncRef, Function, GlobalValue, LibCall, MemFlags, Signature, StackSlot,
+    Type, Value,
 };
 use cranelift_codegen::isa::CallConv;
 use smallvec::SmallVec;
@@ -96,7 +96,8 @@ impl<'a> InterpreterFunctionRef<'a> {
         match self {
             InterpreterFunctionRef::Function(f) => f.stencil.signature.clone(),
             // CallConv here is sort of irrelevant, since we don't use it for anything
-            InterpreterFunctionRef::LibCall(lc) => lc.signature(CallConv::SystemV),
+            // FIXME handle non-64bit systems
+            InterpreterFunctionRef::LibCall(lc) => lc.signature(CallConv::SystemV, types::I64),
         }
     }
 }