diff --git a/releasenotes.md b/releasenotes.md
index 7418a0d3b..140cdb414 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -85,6 +85,7 @@
 - Allow enums to use a distinct type as the backing type.
 - Update addition and subtraction on enums.
 - `@ensure` checks only non-optional results.
+- `assert` may now take varargs for formatting.
  
 ### Stdlib changes
 - Updated posix/win32 stdlib namespacing
diff --git a/src/compiler/compiler_internal.h b/src/compiler/compiler_internal.h
index d817fff83..882d2c9ab 100644
--- a/src/compiler/compiler_internal.h
+++ b/src/compiler/compiler_internal.h
@@ -1374,6 +1374,7 @@ typedef struct
 	bool is_ensure;
 	ExprId message;
 	ExprId expr;
+	Expr **args;
 } AstAssertStmt;
 
 
diff --git a/src/compiler/copying.c b/src/compiler/copying.c
index a0c0d2e60..e272f6a41 100644
--- a/src/compiler/copying.c
+++ b/src/compiler/copying.c
@@ -586,6 +586,7 @@ RETRY:
 		case AST_CT_ASSERT:
 			MACRO_COPY_EXPRID(ast->assert_stmt.expr);
 			MACRO_COPY_EXPRID(ast->assert_stmt.message);
+			MACRO_COPY_EXPR_LIST(ast->assert_stmt.args);
 			break;
 		case AST_BREAK_STMT:
 		case AST_CONTINUE_STMT:
diff --git a/src/compiler/llvm_codegen_stmt.c b/src/compiler/llvm_codegen_stmt.c
index eeb9224aa..84a65aecc 100644
--- a/src/compiler/llvm_codegen_stmt.c
+++ b/src/compiler/llvm_codegen_stmt.c
@@ -1001,16 +1001,28 @@ static inline void llvm_emit_assert_stmt(GenContext *c, Ast *ast)
 		llvm_emit_cond_br(c, &value, on_ok, on_fail);
 		llvm_emit_block(c, on_fail);
 		SourceSpan loc = assert_expr->span;
-		const char *error;
-		if (ast->assert_stmt.message)
+		const char *error = NULL;
+		Expr *message_expr = exprptrzero(ast->assert_stmt.message);
+		BEValue *values = NULL;
+		if (message_expr)
 		{
 			error = exprptr(ast->assert_stmt.message)->const_expr.string.chars;
+			Expr **args = ast->assert_stmt.args;
+			if (vec_size(args))
+			{
+				FOREACH_BEGIN(Expr *arg, args)
+					BEValue var;
+					llvm_emit_expr(c, &var, arg);
+					llvm_emit_any_from_value(c, &var, arg->type);
+					vec_add(values, var);
+				FOREACH_END();
+			}
 		}
 		else
 		{
 			error = "Assert violation";
 		}
-		llvm_emit_panic(c, error, loc, NULL, NULL);
+		llvm_emit_panic(c, values ? NULL : error, loc, values ? error : NULL, values);
 		llvm_emit_br(c, on_ok);
 		llvm_emit_block(c, on_ok);
 	}
diff --git a/src/compiler/parse_stmt.c b/src/compiler/parse_stmt.c
index 95733ecbe..b4ed654dc 100644
--- a/src/compiler/parse_stmt.c
+++ b/src/compiler/parse_stmt.c
@@ -1080,7 +1080,14 @@ static inline Ast *parse_assert_stmt(ParseContext *c)
 
 	if (try_consume(c, TOKEN_COMMA))
 	{
-		ASSIGN_EXPRID_OR_RET(ast->assert_stmt.message, parse_expr(c), poisoned_ast);
+		Expr **args = NULL;
+		ASSIGN_EXPRID_OR_RET(ast->assert_stmt.message, parse_constant_expr(c), poisoned_ast);
+		while (try_consume(c, TOKEN_COMMA))
+		{
+			ASSIGN_EXPR_OR_RET(Expr *expr, parse_expr(c), poisoned_ast);
+			vec_add(args, expr);
+		}
+		ast->assert_stmt.args = args;
 	}
 	TRY_CONSUME_OR_RET(TOKEN_RPAREN, "The ending ')' was expected here.", poisoned_ast);
 	return consume_eos(c, ast);
diff --git a/src/compiler/sema_stmts.c b/src/compiler/sema_stmts.c
index e2c80ff9b..469de3af7 100644
--- a/src/compiler/sema_stmts.c
+++ b/src/compiler/sema_stmts.c
@@ -82,14 +82,12 @@ static inline bool sema_analyse_assert_stmt(SemaContext *context, Ast *statement
 	if (message_expr)
 	{
 		if (!sema_analyse_expr(context, message_expr)) return false;
-		if (!expr_is_const_string(message_expr))
-		{
-			SEMA_ERROR(message_expr, "Expected a string as the error message.");
-			return false;
-		}
+		if (!expr_is_const_string(message_expr)) RETURN_SEMA_ERROR(message_expr, "Expected a string as the error message.");
+		FOREACH_BEGIN(Expr *e, statement->assert_stmt.args)
+			if (!sema_analyse_expr(context, e)) return false;
+		FOREACH_END();
 	}
 
-
 	// Handle force unwrapping using assert, e.g. assert(try x)
 	if (expr->expr_kind == EXPR_TRY_UNWRAP_CHAIN)
 	{
@@ -111,7 +109,7 @@ static inline bool sema_analyse_assert_stmt(SemaContext *context, Ast *statement
 		// If it's ensure (and an error) we print an error.
 		if (statement->assert_stmt.is_ensure)
 		{
-			if (message_expr)
+			if (message_expr && expr_is_const(message_expr) && vec_size(statement->assert_stmt.args))
 			{
 				SEMA_ERROR(expr, "%.*s", EXPAND_EXPR_STRING(message_expr));
 			}
diff --git a/src/version.h b/src/version.h
index 69f43f2d8..f85e77f2b 100644
--- a/src/version.h
+++ b/src/version.h
@@ -1 +1 @@
-#define COMPILER_VERSION "0.4.538"
\ No newline at end of file
+#define COMPILER_VERSION "0.4.539"
\ No newline at end of file
diff --git a/test/test_suite/assert/assertf.c3t b/test/test_suite/assert/assertf.c3t
new file mode 100644
index 000000000..194229887
--- /dev/null
+++ b/test/test_suite/assert/assertf.c3t
@@ -0,0 +1,65 @@
+// #target: macos-x64
+// #safe: yes
+module main;
+
+fn void! main()
+{
+	for (usz i = 0; i < 100000000; i++)
+	{
+		assert(i != 2, "Test %s %s", i, i * 2);
+	}
+}
+
+/* #expect: main.ll
+
+define i64 @main.main() #0 {
+entry:
+  %i = alloca i64, align 8
+  %taddr = alloca i64, align 8
+  %varargslots = alloca [2 x %any], align 16
+  %indirectarg = alloca %"any[]", align 8
+  %reterr = alloca i64, align 8
+  store i64 0, ptr %i, align 8
+  br label %loop.cond
+
+loop.cond:                                        ; preds = %assert_ok, %entry
+  %0 = load i64, ptr %i, align 8
+  %gt = icmp ugt i64 100000000, %0
+  br i1 %gt, label %loop.body, label %loop.exit
+
+loop.body:                                        ; preds = %loop.cond
+  %1 = load i64, ptr %i, align 8
+  %neq = icmp ne i64 2, %1
+  br i1 %neq, label %assert_ok, label %assert_fail
+
+assert_fail:                                      ; preds = %loop.body
+  %2 = insertvalue %any undef, ptr %i, 0
+  %3 = insertvalue %any %2, i64 ptrtoint (ptr @"$ct.ulong" to i64), 1
+  %4 = load i64, ptr %i, align 8
+  %mul = mul i64 %4, 2
+  store i64 %mul, ptr %taddr, align 8
+  %5 = insertvalue %any undef, ptr %taddr, 0
+  %6 = insertvalue %any %5, i64 ptrtoint (ptr @"$ct.long" to i64), 1
+  %7 = getelementptr inbounds [2 x %any], ptr %varargslots, i64 0, i64 0
+  store %any %3, ptr %7, align 16
+  %8 = getelementptr inbounds [2 x %any], ptr %varargslots, i64 0, i64 1
+  store %any %6, ptr %8, align 16
+  %9 = insertvalue %"any[]" undef, ptr %varargslots, 0
+  %10 = insertvalue %"any[]" %9, i64 2, 1
+  store %"any[]" %10, ptr %indirectarg, align 8
+  call void @std.core.builtin.panicf(ptr @.panic_msg, i64 10, ptr @.file, i64 10, ptr @.func, i64 4, i32 7, ptr byval(%"any[]") align 8 %indirectarg)
+  br label %assert_ok
+
+assert_ok:                                        ; preds = %assert_fail, %loop.body
+  %11 = load i64, ptr %i, align 8
+  %neq1 = icmp ne i64 2, %11
+  call void @llvm.assume(i1 %neq1)
+  %12 = load i64, ptr %i, align 8
+  %add = add i64 %12, 1
+  store i64 %add, ptr %i, align 8
+  br label %loop.cond
+
+loop.exit:                                        ; preds = %loop.cond
+  ret i64 0
+}
+