diff --git a/vlib/math/stats/stats.v b/vlib/math/stats/stats.v
index 98d970d2eb5250..402a6b58d3e860 100644
--- a/vlib/math/stats/stats.v
+++ b/vlib/math/stats/stats.v
@@ -50,7 +50,7 @@ pub fn geometric_mean[T](data []T) T {
 		return math.pow(sum, f64(1.0) / data.len)
 	} $else {
 		// use f32 for f32/int/...
-		return T(math.powf(sum, f32(1.0) / data.len))
+		return T(math.powf(f32(sum), f32(1.0) / data.len))
 	}
 }
 
@@ -131,7 +131,7 @@ pub fn rms[T](data []T) T {
 		// use f32 for f32/int/...
 		mut sum := f32(0)
 		for v in data {
-			sum += math.powf(v, 2)
+			sum += math.powf(f32(v), 2)
 		}
 		return T(math.sqrtf(sum / data.len))
 	}
@@ -203,7 +203,7 @@ pub fn population_stddev[T](data []T) T {
 	$if T is f64 {
 		return math.sqrt(population_variance[T](data))
 	} $else {
-		return T(math.sqrtf(population_variance[T](data)))
+		return T(math.sqrtf(f32(population_variance[T](data))))
 	}
 }
 
@@ -218,7 +218,7 @@ pub fn population_stddev_mean[T](data []T, mean T) T {
 	$if T is f64 {
 		return math.sqrt(population_variance_mean[T](data, mean))
 	} $else {
-		return T(math.sqrtf(population_variance_mean[T](data, mean)))
+		return T(math.sqrtf(f32(population_variance_mean[T](data, mean))))
 	}
 }
 
@@ -234,7 +234,7 @@ pub fn sample_stddev[T](data []T) T {
 	$if T is f64 {
 		return math.sqrt(sample_variance[T](data))
 	} $else {
-		return T(math.sqrtf(sample_variance[T](data)))
+		return T(math.sqrtf(f32(sample_variance[T](data))))
 	}
 }
 
diff --git a/vlib/v/ast/table.v b/vlib/v/ast/table.v
index c3b7a25e5ba239..0c6ef498a66ee0 100644
--- a/vlib/v/ast/table.v
+++ b/vlib/v/ast/table.v
@@ -2181,6 +2181,28 @@ pub fn (mut t Table) unwrap_generic_type_ex(typ Type, generic_names []string, co
 			idx := t.find_or_register_map(unwrap_key_type, unwrap_value_type)
 			return new_type(idx).derive_add_muls(typ).clear_flag(.generic)
 		}
+		FnType {
+			mut unwrapped_fn := ts.info.func
+			unwrapped_fn.params = unwrapped_fn.params.clone()
+			mut has_generic := false
+			for i, param in unwrapped_fn.params {
+				if param.typ.has_flag(.generic) {
+					unwrapped_fn.params[i].typ = t.unwrap_generic_type_ex(param.typ, generic_names,
+						concrete_types, recheck_concrete_types)
+					has_generic = true
+				}
+			}
+			if unwrapped_fn.return_type.has_flag(.generic) {
+				unwrapped_fn.return_type = t.unwrap_generic_type_ex(unwrapped_fn.return_type,
+					generic_names, concrete_types, recheck_concrete_types)
+				has_generic = true
+			}
+			if has_generic {
+				idx := t.find_or_register_fn_type(unwrapped_fn, true, false)
+				return new_type(idx).derive_add_muls(typ).clear_flag(.generic)
+			}
+			return typ
+		}
 		Struct, Interface, SumType {
 			if !ts.info.is_generic {
 				return typ
@@ -2423,7 +2445,13 @@ pub fn (mut t Table) unwrap_generic_type_ex(typ Type, generic_names []string, co
 			}
 			return new_type(new_idx).derive(typ).clear_flag(.generic)
 		}
-		else {}
+		else {
+			if typ.has_flag(.generic) {
+				if converted := t.convert_generic_type(typ, generic_names, concrete_types) {
+					return converted
+				}
+			}
+		}
 	}
 	return typ
 }
diff --git a/vlib/v/checker/containers.v b/vlib/v/checker/containers.v
index 2ac098543b091d..b58ecde20134f5 100644
--- a/vlib/v/checker/containers.v
+++ b/vlib/v/checker/containers.v
@@ -314,21 +314,36 @@ fn (mut c Checker) array_init(mut node ast.ArrayInit) ast.Type {
 
 fn (mut c Checker) check_array_init_default_expr(mut node ast.ArrayInit) {
 	mut init_expr := node.init_expr
-	c.expected_type = node.elem_type
+	mut expected_elem_type := node.elem_type
+	if node.elem_type.has_flag(.generic) && c.table.cur_fn != unsafe { nil } {
+		if c.table.cur_fn.generic_names.len > 0
+			&& c.table.cur_concrete_types.len == c.table.cur_fn.generic_names.len {
+			expr := node.init_expr
+			if expr is ast.CallExpr {
+				if func := c.table.find_fn(expr.name) {
+					if !func.return_type.has_flag(.generic) {
+						expected_elem_type = c.table.unwrap_generic_type(node.elem_type,
+							c.table.cur_fn.generic_names, c.table.cur_concrete_types)
+					}
+				}
+			}
+		}
+	}
+	c.expected_type = expected_elem_type
 	init_typ := c.check_expr_option_or_result_call(init_expr, c.expr(mut init_expr))
 	node.init_type = init_typ
-	if !node.elem_type.has_flag(.option) && init_typ.has_flag(.option) {
+	if !expected_elem_type.has_flag(.option) && init_typ.has_flag(.option) {
 		c.error('cannot use unwrapped Option as initializer', init_expr.pos())
 	}
-	if node.elem_type.is_number() && init_typ.is_number() {
+	if expected_elem_type.is_number() && init_typ.is_number() {
 		return
 	}
-	if c.table.type_kind(node.elem_type) == .interface {
-		if c.type_implements(init_typ, node.elem_type, init_expr.pos()) {
+	if c.table.type_kind(expected_elem_type) == .interface {
+		if c.type_implements(init_typ, expected_elem_type, init_expr.pos()) {
 			return
 		}
 	}
-	c.check_expected(init_typ, node.elem_type) or { c.error(err.msg(), init_expr.pos()) }
+	c.check_expected(init_typ, expected_elem_type) or { c.error(err.msg(), init_expr.pos()) }
 }
 
 fn (mut c Checker) check_array_init_para_type(para string, mut expr ast.Expr, pos token.Pos) {
diff --git a/vlib/v/checker/fn.v b/vlib/v/checker/fn.v
index 3d25cdd2b22235..234619944cf404 100644
--- a/vlib/v/checker/fn.v
+++ b/vlib/v/checker/fn.v
@@ -1553,11 +1553,19 @@ fn (mut c Checker) fn_call(mut node ast.CallExpr, mut continue_check &bool) ast.
 			c.error('cannot have parameter after array decompose', node.pos)
 		}
 		param_i := i + nr_multi_values
-		param := if func.is_variadic && i >= func.params.len - 1 {
+		mut param := if func.is_variadic && i >= func.params.len - 1 {
 			func.params.last()
 		} else {
 			func.params[param_i]
 		}
+		if node.is_fn_var && param.typ.has_flag(.generic) && c.table.cur_fn != unsafe { nil }
+			&& c.table.cur_fn.generic_names.len > 0
+			&& c.table.cur_fn.generic_names.len == c.table.cur_concrete_types.len {
+			mut unwrapped := param
+			unwrapped.typ = c.table.unwrap_generic_type(param.typ, c.table.cur_fn.generic_names,
+				c.table.cur_concrete_types)
+			param = unwrapped
+		}
 		// registers if the arg must be passed by ref to disable auto deref args
 		call_arg.should_be_ptr = param.typ.is_ptr() && !param.is_mut
 		if func.is_variadic && call_arg.expr is ast.ArrayDecompose {
diff --git a/vlib/v/checker/tests/generics_fn_param_wrong_arg_type_err.out b/vlib/v/checker/tests/generics_fn_param_wrong_arg_type_err.out
new file mode 100644
index 00000000000000..873ebbf230308b
--- /dev/null
+++ b/vlib/v/checker/tests/generics_fn_param_wrong_arg_type_err.out
@@ -0,0 +1,6 @@
+vlib/v/checker/tests/generics_fn_param_wrong_arg_type_err.vv:2:11: error: cannot use `int literal` as `string` in argument 1 to `f`
+    1 | fn test[T, U](f fn (T) U) U {
+    2 |     return f(1)
+      |              ^
+    3 | }
+    4 |
diff --git a/vlib/v/checker/tests/generics_fn_param_wrong_arg_type_err.vv b/vlib/v/checker/tests/generics_fn_param_wrong_arg_type_err.vv
new file mode 100644
index 00000000000000..e0481fe92c5125
--- /dev/null
+++ b/vlib/v/checker/tests/generics_fn_param_wrong_arg_type_err.vv
@@ -0,0 +1,9 @@
+fn test[T, U](f fn (T) U) U {
+	return f(1)
+}
+
+fn main() {
+	println(test(fn (x string) int {
+		return x.len
+	}))
+}
diff --git a/vlib/v/gen/c/array.v b/vlib/v/gen/c/array.v
index e6aa4676e83031..b2d0f74e639546 100644
--- a/vlib/v/gen/c/array.v
+++ b/vlib/v/gen/c/array.v
@@ -1491,7 +1491,8 @@ fn (mut g Gen) gen_array_wait(node ast.CallExpr) {
 	thread_type := arr.array_info().elem_type
 	thread_sym := g.table.sym(thread_type)
 	thread_ret_type := thread_sym.thread_info().return_type
-	elsymcname := g.table.sym(thread_ret_type).cname
+	unwrapped_ret_type := g.unwrap_generic(thread_ret_type)
+	elsymcname := g.table.sym(unwrapped_ret_type).cname
 	fn_name := g.register_thread_array_wait_call(elsymcname)
 	g.write('${fn_name}(')
 	if node.left_type.is_ptr() {
@@ -1506,7 +1507,8 @@ fn (mut g Gen) gen_fixed_array_wait(node ast.CallExpr) {
 	thread_type := arr.array_fixed_info().elem_type
 	thread_sym := g.table.sym(thread_type)
 	thread_ret_type := thread_sym.thread_info().return_type
-	elsymcname := g.table.sym(thread_ret_type).cname
+	unwrapped_ret_type := g.unwrap_generic(thread_ret_type)
+	elsymcname := g.table.sym(unwrapped_ret_type).cname
 	fn_name := g.register_thread_fixed_array_wait_call(node, elsymcname)
 	g.write('${fn_name}(')
 	g.expr(node.left)
diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 2aec702999f220..e50b0316699429 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -1542,13 +1542,40 @@ fn (mut g Gen) register_thread_void_wait_call() {
 	g.gowrappers.writeln('void __v_thread_wait(__v_thread thread) {')
 	if g.pref.os == .windows {
 		g.gowrappers.writeln('\tu32 stat = WaitForSingleObject(thread, INFINITE);')
+		g.gowrappers.writeln('\tif (stat != WAIT_OBJECT_0) { builtin___v_panic(_S("error waiting thread")); }')
 	} else {
 		g.gowrappers.writeln('\tint stat = pthread_join(thread, (void **)NULL);')
+		g.gowrappers.writeln('\tif (stat != 0) { builtin___v_panic(_S("error waiting thread")); }')
 	}
-	g.gowrappers.writeln('\tif (stat != 0) { builtin___v_panic(_S("unable to join thread")); }')
+	g.gowrappers.writeln('}')
+}
+
+fn (mut g Gen) register_thread_wait_call(eltyp string) {
+	thread_typ := '__v_thread_${eltyp}'
+	fn_name := '${thread_typ}_wait'
+	lock g.waiter_fns {
+		if fn_name in g.waiter_fns {
+			return
+		}
+		g.waiter_fns << fn_name
+		g.waiter_fn_definitions.writeln('${eltyp} ${fn_name}(${thread_typ} thread);')
+	}
+	g.gowrappers.writeln('${eltyp} ${fn_name}(${thread_typ} thread) {')
+	g.gowrappers.writeln('\t${eltyp} res;')
 	if g.pref.os == .windows {
-		g.gowrappers.writeln('\tCloseHandle(thread);')
+		g.gowrappers.writeln('\tu32 stat = WaitForSingleObject(thread.handle, INFINITE);')
+		g.gowrappers.writeln('\tif (stat != WAIT_OBJECT_0) { builtin___v_panic(_S("error waiting thread")); }')
+		g.gowrappers.writeln('\tCloseHandle(thread.handle);')
+		g.gowrappers.writeln('\tres = *(${eltyp}*)(thread.ret_ptr);')
+		g.gowrappers.writeln('\tbuiltin___v_free(thread.ret_ptr);')
+	} else {
+		g.gowrappers.writeln('\tvoid* ret_val;')
+		g.gowrappers.writeln('\tint stat = pthread_join(thread, &ret_val);')
+		g.gowrappers.writeln('\tif (stat != 0) { builtin___v_panic(_S("error waiting thread")); }')
+		g.gowrappers.writeln('\tres = *(${eltyp}*)ret_val;')
+		g.gowrappers.writeln('\tbuiltin___v_free(ret_val);')
 	}
+	g.gowrappers.writeln('\treturn res;')
 	g.gowrappers.writeln('}')
 }
 
@@ -1578,6 +1605,7 @@ void ${fn_name}(${thread_arr_typ} a) {
 	}
 }')
 		} else {
+			g.register_thread_wait_call(eltyp)
 			g.waiter_fn_definitions.writeln('${ret_typ} ${fn_name}(${thread_arr_typ} a);')
 			g.gowrappers.writeln('
 ${ret_typ} ${fn_name}(${thread_arr_typ} a) {
@@ -1620,12 +1648,13 @@ fn (mut g Gen) register_thread_fixed_array_wait_call(node ast.CallExpr, eltyp st
 			g.gowrappers.writeln('
 void ${fn_name}(${thread_arr_typ} a) {
 	for (${ast.int_type_name} i = 0; i < ${len}; ++i) {
-		${thread_typ} t = ((${thread_typ}*)a)[i];
+		${thread_typ} t = a[i];
 		if (t == 0) continue;
 		__v_thread_wait(t);
 	}
 }')
 		} else {
+			g.register_thread_wait_call(eltyp)
 			g.waiter_fn_definitions.writeln('${ret_typ} ${fn_name}(${thread_arr_typ} a);')
 			g.gowrappers.writeln('
 ${ret_typ} ${fn_name}(${thread_arr_typ} a) {
diff --git a/vlib/v/gen/c/spawn_and_go.v b/vlib/v/gen/c/spawn_and_go.v
index c55f68559a832f..bbafb2178f4b1b 100644
--- a/vlib/v/gen/c/spawn_and_go.v
+++ b/vlib/v/gen/c/spawn_and_go.v
@@ -119,8 +119,8 @@ fn (mut g Gen) spawn_and_go_expr(node ast.SpawnExpr, mode SpawnGoMode) {
 		g.expr(arg.expr)
 		g.writeln(';')
 	}
-	call_ret_type := node.call_expr.return_type
-	s_ret_typ := g.styp(call_ret_type)
+	call_ret_type := g.unwrap_generic(node.call_expr.return_type)
+	s_ret_typ := g.styp(g.unwrap_generic(call_ret_type))
 	if g.pref.os == .windows && call_ret_type != ast.void_type {
 		g.writeln('${arg_tmp_var}->ret_ptr = (void *) builtin___v_malloc(sizeof(${s_ret_typ}));')
 	}
@@ -182,14 +182,17 @@ fn (mut g Gen) spawn_and_go_expr(node ast.SpawnExpr, mode SpawnGoMode) {
 	if should_register {
 		g.type_definitions.writeln('\ntypedef struct ${wrapper_struct_name} {')
 		mut fn_var := ''
+		mut wrapper_return_type := call_ret_type
 		if node.call_expr.is_fn_var {
 			fn_sym := g.table.sym(node.call_expr.fn_var_type)
 			info := fn_sym.info as ast.FnType
-			fn_var = g.fn_var_signature(ast.void_type, info.func.return_type, info.func.params.map(it.typ),
+			wrapper_return_type = info.func.return_type
+			fn_var = g.fn_var_signature(ast.void_type, wrapper_return_type, info.func.params.map(it.typ),
 				'fn')
 		} else if node.call_expr.left is ast.AnonFn {
 			f := node.call_expr.left.decl
-			fn_var = g.fn_var_signature(ast.void_type, f.return_type, f.params.map(it.typ),
+			wrapper_return_type = f.return_type
+			fn_var = g.fn_var_signature(ast.void_type, wrapper_return_type, f.params.map(it.typ),
 				'fn')
 		} else {
 			if node.call_expr.is_method {
@@ -198,6 +201,7 @@ fn (mut g Gen) spawn_and_go_expr(node ast.SpawnExpr, mode SpawnGoMode) {
 					mut muttable := unsafe { &ast.Table(g.table) }
 					return_type := muttable.convert_generic_type(f.return_type, f.generic_names,
 						node.call_expr.concrete_types) or { f.return_type }
+					wrapper_return_type = return_type
 					mut arg_types := f.params.map(it.typ)
 					arg_types = arg_types.map(muttable.convert_generic_type(it, f.generic_names,
 						node.call_expr.concrete_types) or { it })
@@ -209,6 +213,7 @@ fn (mut g Gen) spawn_and_go_expr(node ast.SpawnExpr, mode SpawnGoMode) {
 					concrete_types := node.call_expr.concrete_types.map(g.unwrap_generic(it))
 					return_type := g.table.convert_generic_type(f.return_type, f.generic_names,
 						concrete_types) or { f.return_type }
+					wrapper_return_type = return_type
 					mut arg_types := f.params.map(it.typ)
 					arg_types = arg_types.map(g.table.convert_generic_type(it, f.generic_names,
 						concrete_types) or { it })
@@ -230,6 +235,8 @@ fn (mut g Gen) spawn_and_go_expr(node ast.SpawnExpr, mode SpawnGoMode) {
 				}
 			}
 		}
+		wrapper_return_type = g.unwrap_generic(wrapper_return_type)
+		wrapper_s_ret_typ := g.styp(wrapper_return_type)
 		if fn_var != '' {
 			g.type_definitions.writeln('\t${fn_var};')
 		}
@@ -237,7 +244,7 @@ fn (mut g Gen) spawn_and_go_expr(node ast.SpawnExpr, mode SpawnGoMode) {
 			styp := g.styp(expr.receiver_type)
 			g.type_definitions.writeln('\t${styp} arg0;')
 		}
-		need_return_ptr := g.pref.os == .windows && call_ret_type != ast.void_type
+		need_return_ptr := g.pref.os == .windows && wrapper_return_type != ast.void_type
 		for i, arg in expr.args {
 			arg_sym := g.table.sym(arg.typ)
 			if arg_sym.info is ast.FnType {
@@ -256,13 +263,13 @@ fn (mut g Gen) spawn_and_go_expr(node ast.SpawnExpr, mode SpawnGoMode) {
 		thread_ret_type := if g.pref.os == .windows { 'u32' } else { 'void*' }
 		g.waiter_fn_definitions.writeln('${g.static_non_parallel}${thread_ret_type} ${wrapper_fn_name}(${wrapper_struct_name} *arg);')
 		g.gowrappers.writeln('${thread_ret_type} ${wrapper_fn_name}(${wrapper_struct_name} *arg) {')
-		if call_ret_type != ast.void_type {
+		if wrapper_return_type != ast.void_type {
 			if g.pref.os == .windows {
-				g.gowrappers.write_string('\t*((${s_ret_typ}*)(arg->ret_ptr)) = ')
+				g.gowrappers.write_string('\t*((${wrapper_s_ret_typ}*)(arg->ret_ptr)) = ')
 			} else {
-				g.gowrappers.writeln('\t${s_ret_typ}* ret_ptr = (${s_ret_typ}*) builtin___v_malloc(sizeof(${s_ret_typ}));')
+				g.gowrappers.writeln('\t${wrapper_s_ret_typ}* ret_ptr = (${wrapper_s_ret_typ}*) builtin___v_malloc(sizeof(${wrapper_s_ret_typ}));')
 				$if tinyc && arm64 {
-					g.gowrappers.write_string('\t${s_ret_typ} tcc_bug_tmp_var = ')
+					g.gowrappers.write_string('\t${wrapper_s_ret_typ} tcc_bug_tmp_var = ')
 				} $else {
 					g.gowrappers.write_string('\t*ret_ptr = ')
 				}
@@ -355,14 +362,14 @@ fn (mut g Gen) spawn_and_go_expr(node ast.SpawnExpr, mode SpawnGoMode) {
 		}
 		g.gowrappers.writeln(');')
 		$if tinyc && arm64 {
-			if g.pref.os != .windows && call_ret_type != ast.void_type {
+			if g.pref.os != .windows && wrapper_return_type != ast.void_type {
 				g.gowrappers.writeln('\t*ret_ptr = tcc_bug_tmp_var;')
 			}
 		}
 		if is_spawn {
 			g.gowrappers.writeln('\tbuiltin___v_free(arg);')
 		}
-		if g.pref.os != .windows && call_ret_type != ast.void_type {
+		if g.pref.os != .windows && wrapper_return_type != ast.void_type {
 			g.gowrappers.writeln('\treturn ret_ptr;')
 		} else {
 			g.gowrappers.writeln('\treturn 0;')
diff --git a/vlib/v/gen/c/struct.v b/vlib/v/gen/c/struct.v
index 1b4c9bb7e570c5..6515bedcf46601 100644
--- a/vlib/v/gen/c/struct.v
+++ b/vlib/v/gen/c/struct.v
@@ -159,7 +159,12 @@ fn (mut g Gen) struct_init(node ast.StructInit) {
 		} else if is_multiline {
 			g.writeln('(${styp}){')
 		} else if is_generic_default {
-			g.write(g.type_default(node.typ))
+			default_val := g.type_default(node.typ)
+			if default_val == '{0}' {
+				g.write('(${styp}){0}')
+			} else {
+				g.write(default_val)
+			}
 		} else {
 			g.write('(${styp}){')
 		}
diff --git a/vlib/v/tests/comptime/comptime_infix_assign_test.v b/vlib/v/tests/comptime/comptime_infix_assign_test.v
index eb8c08df435d96..b763b7fc44b4e5 100644
--- a/vlib/v/tests/comptime/comptime_infix_assign_test.v
+++ b/vlib/v/tests/comptime/comptime_infix_assign_test.v
@@ -17,7 +17,7 @@ fn enc[T](item T) string {
 			'i64', 'u64' { 16 }
 			else { return '' }
 		}
-		return u64_to_hex(item, len)
+		return u64_to_hex(u64(item), len)
 	} $else $if T is $array {
 		mut hex := ''
 		for val in item {