diff --git a/analyser/module_analyser.c2 b/analyser/module_analyser.c2
index 0ce6e9384..09b99f2f3 100644
--- a/analyser/module_analyser.c2
+++ b/analyser/module_analyser.c2
@@ -28,6 +28,7 @@ import label_vector local;
 import name_vector local;
 import src_loc local;
 import scope;
+import string_buffer;
 import string_pool;
 import warning_flags;
 import struct_func_list as sf_list;
@@ -507,7 +508,24 @@ fn void Analyser.handleStaticAssert(void* arg, StaticAssert* d) {
     Value val2 = ast.evalExpr(rhs);
 
     if (!val1.is_equal(&val2)) {
-        ma.errorRange(rhs.getStartLoc(), rhs.getRange(), "static_assert failed, expected %s, got %s", val1.str(), val2.str());
+        char[256] tmp;
+        string_buffer.Buf buf.init(tmp, elemsof(tmp), false, false, 0);
+        lhs.printLiteral(&buf);
+        buf.add(" == ");
+        rhs.printLiteral(&buf);
+        if (lhs.isLiteral()) {
+            if (rhs.isLiteral()) {
+                ma.errorRange(rhs.getStartLoc(), rhs.getRange(), "static_assert failed: %s", buf.data());
+            } else {
+                ma.errorRange(rhs.getStartLoc(), rhs.getRange(), "static_assert failed: %s, got %s", buf.data(), val2.str());
+            }
+        } else {
+            if (rhs.isLiteral()) {
+                ma.errorRange(lhs.getStartLoc(), lhs.getRange(), "static_assert failed: %s, got %s", buf.data(), val1.str());
+            } else {
+                ma.errorRange(lhs.getStartLoc(), lhs.getRange(), "static_assert failed: %s, got %s and %s", buf.data(), val1.str(), val2.str());
+            }
+        }
     }
 }
 
diff --git a/ast/expr.c2 b/ast/expr.c2
index 6fb570837..57cebb216 100644
--- a/ast/expr.c2
+++ b/ast/expr.c2
@@ -200,6 +200,28 @@ public fn bool Expr.isStringLiteral(const Expr* e) {
     return e.getKind() == ExprKind.StringLiteral;
 }
 
+public fn bool Expr.isLiteral(const Expr* e) {
+    switch (e.getKind()) {
+    case IntegerLiteral:
+    case FloatLiteral:
+    case BooleanLiteral:
+    case CharLiteral:
+    case StringLiteral:
+    case Nil:
+        return true;
+    default:
+        break;
+    }
+    return false;
+}
+
+public fn bool Expr.isComparison(const Expr* e) {
+    if (e.getKind() != BinaryOperator) return false;
+    BinaryOperator* binop = (BinaryOperator*)e;
+    BinaryOpcode opcode = binop.getOpcode();
+    return opcode.isComparison();
+}
+
 public fn bool Expr.isNil(const Expr* e) {
     return e.getKind() == ExprKind.Nil;
 }
diff --git a/generator/c/c_generator.c2 b/generator/c/c_generator.c2
index d943f679e..e9f1c8222 100644
--- a/generator/c/c_generator.c2
+++ b/generator/c/c_generator.c2
@@ -1433,10 +1433,18 @@ const char[] C_defines =
 
 const char[] C2_assert =
     ```c
+    #define va_list __builtin_va_list
+    #define va_start __builtin_va_start
+    #define va_end __builtin_va_end
     int dprintf(int fd, const char *format, ...);
+    int vdprintf(int fd, const char *format, va_list args);
     void abort(void);
-    static int c2_assert(const char* filename, int line, const char* funcname, const char* condstr) {
-        dprintf(2, "%s:%d: function %s: Assertion failed: %s\n", filename, line, funcname, condstr);
+    static int c2_assert(const char* filename, int line, const char* funcname, const char* fmt, ...) {
+        va_list args;
+        va_start(args, fmt);
+        dprintf(2, "%s:%d: function %s: assertion failed: ", filename, line, funcname);
+        vdprintf(2, fmt, args);
+        dprintf(2, "\n");
         abort();
         return 0;
     }
diff --git a/generator/c/c_generator_stmt.c2 b/generator/c/c_generator_stmt.c2
index f23f01fb7..0894d96cf 100644
--- a/generator/c/c_generator_stmt.c2
+++ b/generator/c/c_generator_stmt.c2
@@ -237,26 +237,114 @@ fn void Generator.emitStmt(Generator* gen, Stmt* s, u32 indent, bool newline) {
         gen.emitAsmStmt((AsmStmt*)s, indent);
         break;
     case Assert:
-        if (!gen.enable_asserts) out.print(";//assert");
         AssertStmt* a = (AssertStmt*)s;
-        out.add1('(');
-        Expr* inner = a.getInner();
-        gen.emitExpr(out, inner);
-        out.add1(')');
-        if (gen.enable_asserts) {
-            source_mgr.Location loc = gen.sm.locate(s.getLoc());
-            const char* funcname = gen.cur_function.asDecl().getFullName();
-            out.print(" || c2_assert(\"%s\", %d, \"%s\", \"", loc.filename, loc.line, funcname);
-            // encode expression as a string
-            string_buffer.Buf* str = string_buffer.create(128, false, 0);
-            inner.printLiteral(str);
-            out.encodeBytes(str.data(), str.size(), '"');
-            str.free();
-            out.add("\")");
+        if (!gen.enable_asserts) {
+            out.print(";//assert");
+            out.add1('(');
+            Expr* inner = a.getInner();
+            gen.emitExpr(out, inner);
+            out.add1(')');
+            break;
         }
-        out.add(";\n");
+        gen.emitAssertStmt(a, indent);
+        break;
+    }
+}
+
+fn const char* get_type_format(Expr* e) {
+    QualType qt = e.getType();
+    QualType canon = qt.getCanonicalType();
+    if (canon.isPointer() || canon.isFunction()) return "p";
+    const Type* t = canon.getTypeOrNil();
+    if (canon.isEnum()) {
+        // output numeric value
+        EnumType* et = (EnumType*)t;
+        canon = et.getImplType();
+        t = canon.getTypeOrNil();
+    }
+    const BuiltinType* bi = (BuiltinType*)t;
+    switch (bi.getBaseKind()) {
+    case Char:
+    case Int8:
+    case Int16:
+    case Int32:
+        return "d";
+    case Int64:
+        return "ld";
+    case UInt8:
+    case UInt16:
+    case UInt32:
+        return "u";
+    case UInt64:
+        return "lu";
+    case Float32:
+    case Float64:
+        return "g";
+    case Bool:
+        return "d";
+    case ISize: // not a base kind
+    case USize: // not a base kind
+    case Void:
         break;
     }
+    return nil;
+}
+
+// encode expression as a string
+fn void encode_expression(string_buffer.Buf* out, Expr* e) {
+    char[128] tmp;
+    string_buffer.Buf buf.init(tmp, elemsof(tmp), false, false, 0);
+    e.printLiteral(&buf);
+    const char* s = buf.data();
+    for (const char* p = s;; p++) {
+        if (!*p || *p == '%') {
+            out.encodeBytes(s, (u32)(p - s), '"');
+            if (!*p) break;
+            if (*p == '%') out.add("%%");
+        }
+    }
+}
+
+fn void Generator.emitAssertStmt(Generator* gen, AssertStmt* a, u32 indent) {
+    string_buffer.Buf* out = gen.out;
+    source_mgr.Location loc = gen.sm.locate(((Stmt*)a).getLoc());
+    const char* funcname = gen.cur_function.asDecl().getFullName();
+    Expr* inner = a.getInner();
+    out.add1('(');
+    gen.emitExpr(out, inner);
+    out.print(") || c2_assert(\"%s\", %d, \"%s\", \"", loc.filename, loc.line, funcname);
+    encode_expression(out, inner);
+    if (inner.isComparison()) {
+        BinaryOperator* b = (BinaryOperator*)inner;
+        Expr* lhs = b.getLHS();
+        Expr* rhs = b.getRHS();
+        const char* fmt1 = lhs.isLiteral() ? nil : get_type_format(lhs);
+        const char* fmt2 = rhs.isLiteral() ? nil : get_type_format(rhs);
+        if (fmt1) {
+            out.print(", ");
+            encode_expression(out, lhs);
+            out.print(": %%%s", fmt1);
+        }
+        if (fmt2) {
+            out.print(", ");
+            encode_expression(out, rhs);
+            out.print(": %%%s", fmt2);
+        }
+        out.add1('"');
+        if (fmt1) {
+            out.add(", ");
+            if (*fmt1 == 'p') out.add("(void*)");
+            gen.emitExpr(out, lhs);
+        }
+        if (fmt2) {
+            out.add(", ");
+            if (*fmt2 == 'p') out.add("(void*)");
+            gen.emitExpr(out, rhs);
+        }
+    } else {
+        out.add1('"');
+    }
+    out.add(");\n");
 }
 
 fn void emitAsmPart(string_buffer.Buf* out, bool multi_line, u32 indent) {
diff --git a/test/c_generator/stmts/assert.c2t b/test/c_generator/stmts/assert.c2t
index b5c284aef..2c1b17d07 100644
--- a/test/c_generator/stmts/assert.c2t
+++ b/test/c_generator/stmts/assert.c2t
@@ -6,11 +6,16 @@
 module test;
 
 i32 a = 10;
+i32 b = 20;
 void* p = nil;
 
 public fn i32 main() {
-    assert(a);
     assert(p);
+    assert(a);
+    assert(a == 10);
+    assert(a != 10);
+    assert(a > 10);
+    assert(a == b);
     return 0;
 }
 
@@ -19,8 +24,12 @@ int32_t main(void);
 
 int32_t main(void)
 {
-   (test_a) || c2_assert("file1.c2", 7, "test.main", "a");
    (test_p) || c2_assert("file1.c2", 8, "test.main", "p");
+   (test_a) || c2_assert("file1.c2", 9, "test.main", "a");
+   (test_a == 10) || c2_assert("file1.c2", 10, "test.main", "a == 10, a: %d", test_a);
+   (test_a != 10) || c2_assert("file1.c2", 11, "test.main", "a != 10, a: %d", test_a);
+   (test_a > 10) || c2_assert("file1.c2", 12, "test.main", "a > 10, a: %d", test_a);
+   (test_a == test_b) || c2_assert("file1.c2", 13, "test.main", "a == b, a: %d, b: %d", test_a, test_b);
    return 0;
 }
 
diff --git a/test/globals/static_asserts/static_assert_int.c2 b/test/globals/static_asserts/static_assert_int.c2
index 300613ce9..56e83127f 100644
--- a/test/globals/static_asserts/static_assert_int.c2
+++ b/test/globals/static_asserts/static_assert_int.c2
@@ -1,5 +1,17 @@
 // @warnings{no-unused}
 module test;
 
-static_assert(3, 4);    // @error{static_assert failed, expected 3, got 4}
+static_assert(3, 4);    // @error{static_assert failed: 3 == 4}
+static_assert(0xff, 0b11111110);    // @error{static_assert failed: 0xff == 0b11111110}
 
+type S struct {
+    i32 x, y;
+}
+
+type T struct {
+    u32 x;
+}
+
+static_assert(sizeof(S), 4);    // @error{static_assert failed: sizeof(S) == 4, got 8}
+static_assert(4, sizeof(S));    // @error{static_assert failed: 4 == sizeof(S), got 8}
+static_assert(sizeof(T), sizeof(S));    // @error{static_assert failed: sizeof(T) == sizeof(S), got 4 and 8}