diff --git a/releasenotes.md b/releasenotes.md
index 794380d9c..94c29a966 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -27,6 +27,7 @@
 - Recursive constant definition not properly detected, leading to assert #2780
 - Failed to reject void compile time variables, leading to crash. #2781
 - Inferring the size of a slice with an inner inferred array using {} isn't detected as error #2783
+- Bug in sysv abi when passing union in with floats #2784
 
 ### Fixes
 - Regression with npot vector in struct triggering an assert #2219.
diff --git a/src/compiler/abi/c_abi_x64.c b/src/compiler/abi/c_abi_x64.c
index 0442045ad..3366863af 100644
--- a/src/compiler/abi/c_abi_x64.c
+++ b/src/compiler/abi/c_abi_x64.c
@@ -485,8 +485,13 @@ bool x64_contains_float_at_offset(LoweredType *type, unsigned offset)
 
 static Type *x64_get_fp_type_at_offset(Type *type, unsigned ir_offset)
 {
+	while (type->type_kind == TYPE_UNION)
+	{
+		Decl *decl = type->decl;
+		type = decl->strukt.members[decl->strukt.union_rep]->type;
+	}
 	if (!ir_offset && type_is_float(type)) return type;
-	if (type->type_kind == TYPE_STRUCT || type->type_kind == TYPE_UNION)
+	if (type->type_kind == TYPE_STRUCT)
 	{
 		Decl *element = x64_get_member_at_offset(type->decl, ir_offset);
 		return x64_get_fp_type_at_offset(lowered_member_type(element), ir_offset - element->offset);
diff --git a/test/test_suite/abi/abi_passing_union_with_float.c3t b/test/test_suite/abi/abi_passing_union_with_float.c3t
new file mode 100644
index 000000000..31e994907
--- /dev/null
+++ b/test/test_suite/abi/abi_passing_union_with_float.c3t
@@ -0,0 +1,42 @@
+// #target: linux-x64
+module test;
+union Vec3
+{
+	struct
+	{
+		float x, y, z;
+	}
+	float e;
+}
+fn void test(Vec3)
+{}
+
+fn int main()
+{
+	test((Vec3){1,2,3});
+	return 0;
+}
+/* #expect: test.ll
+
+define void @test.test(<2 x float> %0, float %1) #0 {
+entry:
+  %.anon = alloca %Vec3, align 8
+  store <2 x float> %0, ptr %.anon, align 8
+  %ptradd = getelementptr inbounds i8, ptr %.anon, i64 8
+  store float %1, ptr %ptradd, align 8
+  ret void
+}
+
+; Function Attrs: nounwind uwtable
+define i32 @main() #0 {
+entry:
+  %literal = alloca %Vec3, align 4
+  %coerce = alloca %Vec3, align 8
+  call void @llvm.memcpy.p0.p0.i32(ptr align 4 %literal, ptr align 4 @.__const, i32 12, i1 false)
+  call void @llvm.memcpy.p0.p0.i32(ptr align 8 %coerce, ptr align 4 %literal, i32 12, i1 false)
+  %lo = load <2 x float>, ptr %coerce, align 8
+  %ptradd = getelementptr inbounds i8, ptr %coerce, i64 8
+  %hi = load float, ptr %ptradd, align 8
+  call void @test.test(<2 x float> %lo, float %hi)
+  ret i32 0
+}