diff --git a/vlib/v/gen/c/if.v b/vlib/v/gen/c/if.v
index ea9a80916d1512..92a0665690190e 100644
--- a/vlib/v/gen/c/if.v
+++ b/vlib/v/gen/c/if.v
@@ -378,6 +378,11 @@ fn (mut g Gen) if_expr(node ast.IfExpr) {
 						no_needs_par = true
 					}
 				}
+				inside_casting_to_str_old := g.inside_casting_to_str
+				if !g.inside_casting_to_str && branch.cond is ast.Ident
+					&& g.table.is_interface_var(branch.cond.obj) {
+					g.inside_casting_to_str = true
+				}
 				if no_needs_par {
 					g.write('if ')
 				} else {
@@ -389,6 +394,7 @@ fn (mut g Gen) if_expr(node ast.IfExpr) {
 				} else {
 					g.writeln(') {')
 				}
+				g.inside_casting_to_str = inside_casting_to_str_old
 			}
 		}
 		if needs_tmp_var {
diff --git a/vlib/v/gen/c/infix.v b/vlib/v/gen/c/infix.v
index bbc292f27ed2e3..7ee4f6d4ca3df4 100644
--- a/vlib/v/gen/c/infix.v
+++ b/vlib/v/gen/c/infix.v
@@ -1055,6 +1055,13 @@ fn (mut g Gen) gen_plain_infix_expr(node ast.InfixExpr) {
 	}
 	if node.left_type.is_ptr() && node.left.is_auto_deref_var() {
 		g.write('*')
+	} else if !g.inside_casting_to_str && node.left is ast.Ident
+		&& g.table.is_interface_var(node.left.obj) {
+		inside_casting_to_str_old := g.inside_casting_to_str
+		g.inside_casting_to_str = true
+		defer {
+			g.inside_casting_to_str = inside_casting_to_str_old
+		}
 	}
 	g.expr(node.left)
 	g.write(' ${node.op.str()} ')
diff --git a/vlib/v/tests/interface_var_test.v b/vlib/v/tests/interface_var_test.v
new file mode 100644
index 00000000000000..196d5ecdbe7e19
--- /dev/null
+++ b/vlib/v/tests/interface_var_test.v
@@ -0,0 +1,28 @@
+interface Param {}
+
+fn test_main() {
+	param := Param(false)
+
+	match param {
+		bool {
+			println(param) // &false
+			println(param == true) // false
+			println(param == false) // true
+			if param {
+				assert false
+			}
+			if !param {
+				assert true
+			}
+			if param == true {
+				assert false
+			}
+			if param == false {
+				assert true
+			}
+		}
+		else {
+			return
+		}
+	}
+}