diff --git a/ext/bigdecimal/bigdecimal.c b/ext/bigdecimal/bigdecimal.c
index c15099ff..c64c6e24 100644
--- a/ext/bigdecimal/bigdecimal.c
+++ b/ext/bigdecimal/bigdecimal.c
@@ -2846,6 +2846,8 @@ rb_cstr_convert_to_BigDecimal(const char *c_str, int raise_exception)
 static inline VALUE
 rb_str_convert_to_BigDecimal(VALUE val, int raise_exception)
 {
+    StringValue(val);
+    rb_must_asciicompat(val);
     if (!raise_exception && memchr(RSTRING_PTR(val), '\0', RSTRING_LEN(val))) return Qnil;
     const char *c_str = StringValueCStr(val);
     VALUE bd = rb_cstr_convert_to_BigDecimal(c_str, raise_exception);
@@ -3012,6 +3014,12 @@ f_BigDecimal(int argc, VALUE *argv, VALUE self)
 static VALUE
 BigDecimal_s_interpret_loosely(VALUE klass, VALUE str)
 {
+    StringValue(str);
+    rb_must_asciicompat(str);
+    /* Like String#to_f, ignore everything after an embedded NUL */
+    const char *p = RSTRING_PTR(str);
+    const char *nul = memchr(p, '\0', RSTRING_LEN(str));
+    if (nul) str = rb_str_subseq(str, 0, nul - p);
     char const *c_str = StringValueCStr(str);
     NULLABLE_BDVALUE v = CreateFromString(c_str, klass, false, true);
     RB_GC_GUARD(str);
diff --git a/test/bigdecimal/test_bigdecimal.rb b/test/bigdecimal/test_bigdecimal.rb
index 5bfd98cf..a24bdbcc 100644
--- a/test/bigdecimal/test_bigdecimal.rb
+++ b/test/bigdecimal/test_bigdecimal.rb
@@ -113,6 +113,12 @@ def test_BigDecimal_issue_192
     assert_equal(BigDecimal(int), big, "[ruby/bigdecimal#192]")
   end
 
+  def test_BigDecimal_with_ascii_incompatible_string
+    str = "123".encode("UTF-16LE")
+    assert_raise(Encoding::CompatibilityError) { BigDecimal(str) }
+    assert_raise(Encoding::CompatibilityError) { BigDecimal(str, exception: false) }
+  end
+
   def test_BigDecimal_with_invalid_string
     [
       '', '.', 'e1', 'd1', '.e', '.d', '1.e', '1.d', '.1e', '.1d',
diff --git a/test/bigdecimal/test_bigdecimal_util.rb b/test/bigdecimal/test_bigdecimal_util.rb
index e2ead321..67693935 100644
--- a/test/bigdecimal/test_bigdecimal_util.rb
+++ b/test/bigdecimal/test_bigdecimal_util.rb
@@ -125,6 +125,9 @@ def test_String_to_d
     assert_equal(BigDecimal('1.2'), "1.2.3".to_d)
     assert_equal(BigDecimal('1'), "1.".to_d)
     assert_equal(BigDecimal('1'), "1e".to_d)
+    assert_equal(BigDecimal('1'), "1\0 2".to_d)
+    assert_equal(BigDecimal('0'), "\0 1".to_d)
+    assert_raise(Encoding::CompatibilityError) { "1".encode("UTF-16LE").to_d }
 
     assert("2.5".to_d.frozen?)
   end