diff --git a/py/compile.c b/py/compile.c
index b2000d5b09..dc5a8b38a2 100644
--- a/py/compile.c
+++ b/py/compile.c
@@ -145,7 +145,9 @@ mp_parse_node_t fold_constants(mp_parse_node_t pn) {
                     } else if (MP_PARSE_NODE_IS_TOKEN_KIND(pns->nodes[1], MP_TOKEN_OP_PERCENT)) {
                         pn = mp_parse_node_new_leaf(MP_PARSE_NODE_SMALL_INT, python_modulo(arg0, arg1));
                     } else if (MP_PARSE_NODE_IS_TOKEN_KIND(pns->nodes[1], MP_TOKEN_OP_DBL_SLASH)) {
-                        pn = mp_parse_node_new_leaf(MP_PARSE_NODE_SMALL_INT, python_floor_divide(arg0, arg1));
+                        if (arg1 != 0) {
+                            pn = mp_parse_node_new_leaf(MP_PARSE_NODE_SMALL_INT, python_floor_divide(arg0, arg1));
+                        }
                     } else {
                         // shouldn't happen
                         assert(0);
diff --git a/py/obj.c b/py/obj.c
index f80d1a9772..95052d16d2 100644
--- a/py/obj.c
+++ b/py/obj.c
@@ -62,7 +62,7 @@ void mp_obj_print_exception(mp_obj_t exc) {
             }
         }
     }
-    mp_obj_print(exc, PRINT_REPR);
+    mp_obj_print(exc, PRINT_EXC);
     printf("\n");
 }
 
diff --git a/py/obj.h b/py/obj.h
index a34d5407af..952187e464 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -141,7 +141,9 @@ typedef mp_obj_t (*mp_fun_var_t)(uint n, const mp_obj_t *);
 typedef mp_obj_t (*mp_fun_kw_t)(uint n, const mp_obj_t *, mp_map_t *);
 
 typedef enum {
-    PRINT_STR, PRINT_REPR
+    PRINT_STR,
+    PRINT_REPR,
+    PRINT_EXC, // Special format for printing exception in unhandled exception message
 } mp_print_kind_t;
 
 typedef void (*mp_print_fun_t)(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t o, mp_print_kind_t kind);
diff --git a/py/objexcept.c b/py/objexcept.c
index 7dd5c7ac39..0efc21d360 100644
--- a/py/objexcept.c
+++ b/py/objexcept.c
@@ -11,42 +11,34 @@
 #include "runtime.h"
 #include "runtime0.h"
 
-// This is unified class for C-level and Python-level exceptions
-// Python-level exceptions have empty ->msg and all arguments are in
-// args tuple. C-level exceptions likely have ->msg set, and args is empty.
 typedef struct _mp_obj_exception_t {
     mp_obj_base_t base;
     mp_obj_t traceback; // a list object, holding (file,line,block) as numbers (not Python objects); a hack for now
-    vstr_t *msg;
     mp_obj_tuple_t args;
 } mp_obj_exception_t;
 
 // Instance of GeneratorExit exception - needed by generator.close()
 // This would belong to objgenerator.c, but to keep mp_obj_exception_t
 // definition module-private so far, have it here.
-const mp_obj_exception_t mp_const_GeneratorExit_obj = {{&mp_type_GeneratorExit}, MP_OBJ_NULL, NULL, {{&mp_type_tuple}, 0}};
+const mp_obj_exception_t mp_const_GeneratorExit_obj = {{&mp_type_GeneratorExit}, MP_OBJ_NULL, {{&mp_type_tuple}, 0}};
 
 STATIC void mp_obj_exception_print(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t o_in, mp_print_kind_t kind) {
     mp_obj_exception_t *o = o_in;
-    if (o->msg != NULL) {
-        print(env, "%s: %s", qstr_str(o->base.type->name), vstr_str(o->msg));
-    } else {
-        // Yes, that's how CPython has it
-        // TODO now that exceptions are classes and instances, I think this needs to be changed to match CPython
-        if (kind == PRINT_REPR) {
-            print(env, "%s", qstr_str(o->base.type->name));
-        }
-        if (kind == PRINT_STR) {
-            if (o->args.len == 0) {
-                print(env, "");
-                return;
-            } else if (o->args.len == 1) {
-                mp_obj_print_helper(print, env, o->args.items[0], PRINT_STR);
-                return;
-            }
-        }
-        tuple_print(print, env, &o->args, kind);
+    if (kind == PRINT_REPR) {
+        print(env, "%s", qstr_str(o->base.type->name));
+    } else if (kind == PRINT_EXC) {
+        print(env, "%s: ", qstr_str(o->base.type->name));
     }
+    if (kind == PRINT_STR || kind == PRINT_EXC) {
+        if (o->args.len == 0) {
+            print(env, "");
+            return;
+        } else if (o->args.len == 1) {
+            mp_obj_print_helper(print, env, o->args.items[0], PRINT_STR);
+            return;
+        }
+    }
+    tuple_print(print, env, &o->args, kind);
 }
 
 STATIC mp_obj_t mp_obj_exception_make_new(mp_obj_t type_in, uint n_args, uint n_kw, const mp_obj_t *args) {
@@ -59,7 +51,6 @@ STATIC mp_obj_t mp_obj_exception_make_new(mp_obj_t type_in, uint n_args, uint n_
     mp_obj_exception_t *o = m_new_obj_var(mp_obj_exception_t, mp_obj_t, n_args);
     o->base.type = type;
     o->traceback = MP_OBJ_NULL;
-    o->msg = NULL;
     o->args.base.type = &mp_type_tuple;
     o->args.len = n_args;
     memcpy(o->args.items, args, n_args * sizeof(mp_obj_t));
@@ -185,7 +176,7 @@ MP_DEFINE_EXCEPTION(Exception, BaseException)
     */
 
 mp_obj_t mp_obj_new_exception(const mp_obj_type_t *exc_type) {
-    return mp_obj_new_exception_msg_varg(exc_type, NULL);
+    return mp_obj_new_exception_args(exc_type, 0, NULL);
 }
 
 mp_obj_t mp_obj_new_exception_args(const mp_obj_type_t *exc_type, uint n_args, const mp_obj_t *args) {
@@ -202,22 +193,25 @@ mp_obj_t mp_obj_new_exception_msg_varg(const mp_obj_type_t *exc_type, const char
     assert(exc_type->make_new == mp_obj_exception_make_new);
 
     // make exception object
-    mp_obj_exception_t *o = m_new_obj_var(mp_obj_exception_t, mp_obj_t, 0);
+    mp_obj_exception_t *o = m_new_obj_var(mp_obj_exception_t, mp_obj_t, 1);
     o->base.type = exc_type;
     o->traceback = MP_OBJ_NULL;
     o->args.base.type = &mp_type_tuple;
-    o->args.len = 0;
+    o->args.len = 1;
 
     if (fmt == NULL) {
         // no message
-        o->msg = NULL;
+        assert(0);
     } else {
-        // render exception message
-        o->msg = vstr_new();
+        // render exception message and store as .args[0]
+        // TODO: optimize bufferbloat
+        vstr_t *vstr = vstr_new();
         va_list ap;
         va_start(ap, fmt);
-        vstr_vprintf(o->msg, fmt, ap);
+        vstr_vprintf(vstr, fmt, ap);
         va_end(ap);
+        o->args.items[0] = mp_obj_new_str((byte*)vstr->buf, vstr->len, false);
+        vstr_free(vstr);
     }
 
     return o;
diff --git a/py/objfloat.c b/py/objfloat.c
index babc0c479b..3916c340b3 100644
--- a/py/objfloat.c
+++ b/py/objfloat.c
@@ -1,4 +1,6 @@
 #include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
 #include <assert.h>
 #include <math.h>
 
@@ -23,7 +25,13 @@ STATIC void float_print(void (*print)(void *env, const char *fmt, ...), void *en
     format_float(o->value, buf, sizeof(buf), 'g', 6, '\0');
     print(env, "%s", buf);
 #else
-    print(env, "%.8g", (double) o->value);
+    char buf[32];
+    sprintf(buf, "%.8g", (double) o->value);
+    print(env, buf);
+    if (strchr(buf, '.') == NULL) {
+        // Python floats always have decimal point
+        print(env, ".0");
+    }
 #endif
 }
 
@@ -103,13 +111,15 @@ mp_obj_t mp_obj_float_binary_op(int op, mp_float_t lhs_val, mp_obj_t rhs_in) {
         case MP_BINARY_OP_INPLACE_SUBTRACT: lhs_val -= rhs_val; break;
         case MP_BINARY_OP_MULTIPLY:
         case MP_BINARY_OP_INPLACE_MULTIPLY: lhs_val *= rhs_val; break;
-        /* TODO floor(?) the value
+        // TODO: verify that C floor matches Python semantics
         case MP_BINARY_OP_FLOOR_DIVIDE:
-        case MP_BINARY_OP_INPLACE_FLOOR_DIVIDE: val = lhs_val / rhs_val; break;
-        */
+        case MP_BINARY_OP_INPLACE_FLOOR_DIVIDE:
+            lhs_val = MICROPY_FLOAT_C_FUN(floor)(lhs_val / rhs_val);
+            goto check_zero_division;
         case MP_BINARY_OP_TRUE_DIVIDE:
         case MP_BINARY_OP_INPLACE_TRUE_DIVIDE: 
             lhs_val /= rhs_val; 
+check_zero_division:
             if (isinf(lhs_val)){ // check for division by zero
                 nlr_jump(mp_obj_new_exception_msg(&mp_type_ZeroDivisionError, "float division by zero"));
             }
@@ -119,7 +129,8 @@ mp_obj_t mp_obj_float_binary_op(int op, mp_float_t lhs_val, mp_obj_t rhs_in) {
         case MP_BINARY_OP_LESS_EQUAL: return MP_BOOL(lhs_val <= rhs_val);
         case MP_BINARY_OP_MORE_EQUAL: return MP_BOOL(lhs_val >= rhs_val);
 
-        return NULL; // op not supported
+        default:
+            return NULL; // op not supported
     }
     return mp_obj_new_float(lhs_val);
 }
diff --git a/py/runtime.c b/py/runtime.c
index 7e02879455..f827fd831e 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -348,13 +348,20 @@ mp_obj_t mp_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
                 }
                 case MP_BINARY_OP_FLOOR_DIVIDE:
                 case MP_BINARY_OP_INPLACE_FLOOR_DIVIDE:
-                {
+                    if (rhs_val == 0) {
+                        goto zero_division;
+                    }
                     lhs_val = python_floor_divide(lhs_val, rhs_val);
                     break;
-                }
+
                 #if MICROPY_ENABLE_FLOAT
                 case MP_BINARY_OP_TRUE_DIVIDE:
-                case MP_BINARY_OP_INPLACE_TRUE_DIVIDE: return mp_obj_new_float((mp_float_t)lhs_val / (mp_float_t)rhs_val);
+                case MP_BINARY_OP_INPLACE_TRUE_DIVIDE:
+                    if (rhs_val == 0) {
+zero_division:
+                        nlr_jump(mp_obj_new_exception_msg(&mp_type_ZeroDivisionError, "division by zero"));
+                    }
+                    return mp_obj_new_float((mp_float_t)lhs_val / (mp_float_t)rhs_val);
                 #endif
 
                 case MP_BINARY_OP_MODULO:
diff --git a/tests/basics/float1.py b/tests/basics/float1.py
index 200d955856..bf1305c3d5 100644
--- a/tests/basics/float1.py
+++ b/tests/basics/float1.py
@@ -1,3 +1,16 @@
 # basic float
 x = 1 / 2
 print(x)
+
+print(1.0 // 2)
+print(2.0 // 2)
+
+try:
+    1.0 / 0
+except ZeroDivisionError:
+    print("ZeroDivisionError")
+
+try:
+    1.0 // 0
+except ZeroDivisionError:
+    print("ZeroDivisionError")
diff --git a/tests/basics/int-divzero.py b/tests/basics/int-divzero.py
new file mode 100644
index 0000000000..d1fc579321
--- /dev/null
+++ b/tests/basics/int-divzero.py
@@ -0,0 +1,9 @@
+try:
+    1 / 0
+except ZeroDivisionError:
+    print("ZeroDivisionError")
+
+try:
+    1 // 0
+except ZeroDivisionError:
+    print("ZeroDivisionError")